The Brain and Nervous System

The Human Nervous System is a complex combination of neurons that enables the brain to

obtain information about what is happening inside and outside of the body and to thus, allow

the brain to respond appropriately.

The human nervous system branches out into two other nervous systems: Central nervous

system (CNS) and Peripheral nervous system (PNS).

Central Nervous System comprises the brain and spinal cord

The main role of the CNS is to: integrate all the information coming from various parts of

the body, coordinate different activities in the body, and controlling behaviour.

The brain organises, integrates and interprets information

The spinal cord runs from the base of the brain (brain stem), through the bones in the

spine (vertebrae) until the middle section of the spine. The spinal cord plays a pivotal

role in that it conveys messages from the brain to the PNS, and from the PNS to the brain

[damage to the spinal cord can lead to shock or paralysis – as messages cannot be

conveyed for movement to occur]

The spinal cord is also segmented; meaning the upper part of the spinal cord is

responsible for communication between the brain and the upper parts of the body,

whereas the lower part of the spinal cord is responsible for communication between the

brain and the lower parts of the body, such as legs, toes and feet.

Peripheral Nervous system includes all parts of the nervous system that lie outside the

brain and spinal cord. Its primary role is to connect the CNS to the body’s organs, muscles

and glands [such as skin and limbs]. It does this in two specific ways:

The PNS communicates information from the body’s organs, muscles, and glands

to the CNS. The PNS also communicates information from the outside of the body

(such as environmental temperature, via sensory neurons) and also

communicates information from inside the body to the CNS (such as internal

aches and pains)

Example: This sort of communication occurs when you hold a hot mug of tea

The PNS communicates information from the CNS to the body’s organs, muscles

and glands (via motor neurons) Example: This sort of communication occurs when you want to move your hand to pat a dog

In both the above cases, the PNS acts as a sort of carrier of information for

communication to occur between the CNS and the body’s organs, muscles and

glands.

The peripheral nervous system then has two subdivisions: The Somatic

Nervous system and Autonomic Nervous System.

o Somatic nervous system

o Main role: Responsible for carrying sensory and motor information to and from

the CNS. Also associated with emotional responses such as crying and sweating.

Also, the Somatic N.S. is responsible for the voluntary movement of skeletal

muscles

o When an organism intends to move a muscle at any given moment, motor

neurons (nerves) are carried by the PNS (or more specifically by the Somatic

N.S.) to the muscles where the movement will take place. The CNS and PNS

work together to allow an organism to interact with its environment. For

example, when a girl pats a dog, motor neurons are carried by the PNS from

her brain to her muscles that allow the girl to move her arms and hand to pat

the dog. When the child pats the dog, the sensation of feeling the dog’s fur is

detected by the sensory receptors and this sensory information (in the form

of sensory neurons) is carried by the PNS to the brain. In the brain, this

information (sensation of dog’s fur on child’s hand) is sent to a specific

cortex where it is interpreted as being “soft”.

o Autonomic nervous system is the part of the PNS that connects the CNS to

the body’s organs, muscles and glands. Its main role is to control involuntary

body functions such as heartbeat, blood flow, respiration, and digestion. The

autonomic nervous system is responsible for the communication of

information between the CNS and the body’s non-skeletal muscles, as well as

the internal glands and organs that carry out basic functions for survival,

such as heartbeat or digestion. The Autonomic nervous system is self-

regulating and “autonomous”; it operates without voluntary control or

conscious awareness; for example when we breathe or when our heart beats,

we are not controlling these actions, neither are we consciously aware of

each and every breathe we take, or every heartbeat that occurs in us.

The autonomic nervous system is then divided into two sub divisions:

Sympathetic nervous system and Parasympathetic nervous system.

The sympathetic nervous system controls the body’s response to emergencies

and acts like an emergency system that activates in us the moment we are faced

with danger, fear, or anxiety. The Sympathetic N.S. prepares the body for action.

The sympathetic nervous system is essential for survival, as when we are faced

with fear; our sympathetic nervous system prepares our body to either fight or

flight (run away). This is known as the flight-fight response

On the other hand, the parasympathetic nervous system activates in moments

where fear or danger is no longer present; that is, the parasympathetic nervous

system calms the body after action. The parasympathetic nervous system is also

responsible for maintaining normal automatic day-to-day body functioning, such

as digestion, normal heart rate and normal breathing. For this reason, the

parasympathetic nervous system also plays a vital role in maintaining

homeostasis (normal body functioning within narrow limits or conditions).

Both the sympathetic and parasympathetic nervous systems affect the same

tissues and organs; however, they do so in different ways. The parasympathetic

nervous system ensures that our body remains calm in situations of low arousal

or fear, and that the stability of our normal bodily functioning (homeostasis) is

maintained. The sympathetic nervous system, then prepares these same tissues

and organs to respond effectively to any threat or danger that may arise in the

organism’s environment.

The brain is composed of 3 parts; the forebrain, midbrain and the hindbrain.

Forebrain: contains hypothalamus, thalamus and cerebrum

Responsible for higher order thinking, problem solving ability, planning ability,

memory, language, emotions, and some body movement.

Midbrain: links the hindbrain with the forebrain

Contains the Reticular Activating System (RAS) which regulates arousal levels,

including attention and consciousness (whether we are alert, awake, drowsy or

sleepy)

Hindbrain: is the link between the spinal cord and the brain. Plays an important role in

movement and balance.

The hindbrain contains the brain stem, cerebellum, pons, parts of the reticular

formation and medulla.

The brain is referred to as the master organ because it is responsible for pretty much

everything we think, feel and do.

The brain is encased in a hard protective skull

The brain weighs about 1.5 kg

The brain’s consistency is similar to that of firm jelly & is covered by a strong membrane

There is a small gap between brain and skull: gap is filled with fluid; and acts like a

cushion against knocks or bumps on the head, thereby protecting the brain from

damage

The brain is made up of billions of neurons; these neurons make trillions of connections;

and these connections are the means by which information is transmitted between

neurons

Cerebral Hemispheres of the brain are two almost symmetrical brain structures that make up

the two “halves” of the brain. They appear to be separated by a deep groove (longitudinal

fissure) that runs from the back to the front of the brain. However, the hemispheres are not

completely separated, as they are joined at several points by bundles of nerve tissue. The largest

and most important of these bundles of nerve tissue is known as the corpus callosum.

Corpus Callosum is a band of nerve tissue that separates the left and right hemispheres of the

brain. The corpus callosum also serves as the main communication pathway between them, so

that interaction between the left and right hemisphere can occur.

In short, the corpus callosum acts as a ‘bridge’ for neural messages that are sent

between the two hemispheres of the brain

The corpus callosum is about 10cm in length and 0.75cm in thickness

Cerebral Cortex

In Latin, the word ‘cortex’ means ‘outer covering’ of a tree.

Similarly, when we speak of the brain, the cerebral cortex is also basically an outer covering of

the brain. The cerebral cortex is the convoluted (folded) outer covering of the two

hemispheres of the brain.

o Only about 2-4 mm thick

o Contains ¾ of the brain’s neurons

o Has a large surface area if unfolded (to allow for more neural

transmission)

o Involved with information processing activities such as; memory,

perception, language, problem solving, learning, thinking, and the

planning and control of voluntary body movements

Areas of cerebral cortex and their main functions

Sensory cortex: receive and process information from our different senses

Motor cortex: receives, processes and sends information about voluntary body movements

Association cortex: integrate sensory, motor & other information; and are involved in more

complex mental abilities, such as problem solving, perceiving and thinking

Four lobes of the cerebral cortex

The cerebral cortex of each hemisphere comprises 4 lobes:

Frontal, Parietal, Occipital, and Temporal

Each of the 4 lobes of the cerebral cortex have specialised areas that receive and process sensory or motor information. Frontal Lobe

The largest of the four lobes Occupies the upper forward half of each cerebral hemisphere, right behind your

forehead Specialised area: Primary motor cortex; controls skeletal muscles; controls voluntary

body movements Primary motor cortex in left frontal lobe = controls movements on right side of body,

etc. The amount of cortex provided to a particular body part depends on the ‘complexity’ or

‘fineness’ of the movement. For e.g. Body parts we can move with the greatest precision (such as fingers and tongue) take up more cortical space than those body parts over which we have less control (such as shoulders and the thigh)

Frontal lobe is also involved in: attention, personality, control and expression of emotions

Broca’s area is located in the left frontal lobe- and allows for fluency of speech (speech production)

CASE STUDY: Phineas Gage: Phineas Gage was involved in a serious accident at work. A metal rod thrust through his skull behind the eye socket, penetrating the prefrontal cortex of his frontal lobe. Miraculously, he survived the accident and was able to speak and move because the motor cortex and Broca’s area of his frontal lobe had not been affected. However, Gage was left with permanent brain damage to his prefrontal cortex. This brain damage caused personality changes; Gage went from being a calm, polite and responsible man (before the accident), to becoming a man who was emotionally unstable, rude, irresponsible, incapable of making good judgments and carrying out planned behaviours; his personality changed to such an extent that his friends claimed he was “no longer Gage”.

Larger Cerebral Cortex = Greater capability of behaviour that is regarded as “intelligent” (i.e. problem solving, thinking)

Parietal Lobe

Located right behind the frontal lobe Processes sensory information from the body and the skin senses Specialised area: Primary somatosensory cortex; receives and processes sensory

information from the skin and body, allowing us to perceive / experience bodily sensations

This sensory information could be touch, pressure, temperature (from sensory receptors in skin), info about muscle movement, position of limbs from sensory receptors in muscles

Primary somatosensory cortex on left side = receives and processes sensory information from right side of body

The amount of cortex devoted to a particular body part depends on the sensitivity and amount of use of that body part (for example: more cortex would be devoted to our fingers as we use our fingers a lot)

Occipital Lobe

Known as the “main centre for visual processing” Located at the rearmost area of each cerebral hemisphere; at the back of your head Exclusively responsible for the sense of vision Specialised area: Primary Visual cortex; major destination of visual information coming

from the two eyes. Each hemisphere receives and processes half of this visual information. Damage to the occipital lobe blindness (even if the eyes and their neural

connections to the brain are normal)

Temporal Lobe

Located in the lower central area of the brain; above and around the top of each ear Temporal lobe = primarily involved with processing and interpreting auditory stimuli Temporal lobe also plays an important role in memory (as each temporal lobe contains a

hippocampus), in our ability to identify and recognise faces, in our emotional response to sensory information and memories, language, meaning, memory and learning

Specialised area: Primary auditory cortex- receives and processes sounds from both ears Damage to temporal lobes = amnesia (partial or complete loss of memory) Wernicke’s area is located in the left temporal lobe; involved mainly in speech

comprehension (how we understand and make sense of words and speech) Damage to Wernicke’s area = impairment in the ability to produce meaningful

understandable speech; fluency of speech is good, but what is said does not make sense; like a “word salad”

Generally, both hemispheres of the brain appear to be exact replicas of each other, in terms of size, shape and function. However, each hemisphere also has specialised functions that are exclusive to that particular hemisphere only. It is also important to understand that the left and right hemispheres are actually involved in nearly all functions; and that both hemispheres act together in an interactive and coordinated way.

The LEFT hemisphere specialises in verbal functions and analytical functions.

The RIGHT hemisphere specialises in non-verbal functions.

The reticular formation is a part of the reticular activating system that goes through the centre of the brain stem, through the midbrain, to the forebrain (under the cerebral cortex). In 1949, Moruzzi and Magnoun conducted an experiment where they electrically stimulated the reticular formation of cats. Once they did this, the cats suddenly became awake and alert. Conversely, when they cut off the connections between the reticular formation and the rest of the brain, the cats fell into a prolonged coma and they stayed this way until they died. The Reticular Activating System (RAS) is a network of neurons that extends in many different directions from the reticular formation, going to the different areas of the brain and spinal cord Its ‘ascending tracts’ (upward nerve pathways) extend to the cerebral cortex Its ‘descending tracts’ (downward nerve pathways) extend to the spinal cord Major functions of the RAS:

Regulate cortical arousal (alertness) Influencing whether we are awake, drowsy, asleep or in some state in between

o When our RAS is less active, we go to sleep.

o Because the RAS is associated with alertness and arousal, we can say that many

anaesthetics used in surgery work to reduce the activity and influence of the RAS, rendering a person unconscious.

o Furthermore, damage to the RAS can severely disrupt our sleep-wake cycle and

because damage to the RAS can also damage our alertness, often severe enough damage to the RAS can cause a person to go into a coma or a vegetative state.

o In the maintenance and regulation of cortical arousal, the RAS also influences attention and more so, influences what we CHOOSE TO ATTEND; that is; the RAS influences selective attention.

Neurons of the RAS send out a steady stream of impulses that keep the cerebral cortex active and alert; taking account of the incoming flow of sensory and motor information. The RAS can highlight certain neural information that is of particular importance, and in this way our RAS can direct our attention and consciousness towards potentially significant events. For example; when a driver is tired and driving and suddenly sees a cow on the road, his RAS will bombard the cerebral cortex with stimulation so that specific cortical areas (relating to alertness) can be aroused and the driver won’t run over the cow. Our RAS can also detect and filter out certain incoming weak sensory information, so that we are able to focus on a particular stimulus. ~~~ Another way in which sensory information can be routed to the cerebral cortex is through the thalamus. The thalamus and RAS don’t work independent of one another; the ascending RAS tracts connect to central areas of the thalamus – both influencing arousal and attention through the thalamus. REMEMBER: The thalamus receives all information from our senses, EXCEPT smell. The thalamus is a brain structure that filters information from the senses and transmits or ‘relays’ it to the cerebral cortex. The thalamus is located at the top of the brain stem, deep within the cerebral hemispheres. The thalamus is divided into two egg shaped parts, which sit side by side, one being in each of the hemispheres. The thalamus serves two main roles:

It receives incoming sensory information and transmits this information to the cerebral cortex; where it is then sent to a relevant cortex for the sensory information to be processed.

For example: if you saw a cute colourful coffee mug, your eye’s sensory (visual) receptors would first detect the colour of it… this sensory information would then travel to the thalamus; and the thalamus would then transmit this information to the specific cortex (in this case, the occipital lobe and the visual cortex) and we would then perceive and say to ourselves that “heyy that’s a really colourful mug! ”

The thalamus also plays an important role in attention. The thalamus actively filters large amounts of information; giving more importance to some information and less emphasis to others. Research using PET scanning has indicated that, when people pay attention to specific sensory information, certain parts of the reticular formation and the thalamus are active. This sensory information is then sent to the relevant part of the cortex; which then communicates back to another part of the thalamus; indicating which parts of the stimulus to attend to and which parts to ignore.

This may be the reason why people with damage to certain areas (associated with attention) in the thalamus may experience difficulty filtering stimuli; that is, attending to one task while ignoring another task.

Furthermore, because the thalamus is connected to the reticular formation and nerve pathways of the reticular formation; the thalamus plays an important role in regulating arousal.

Damage to these areas (associated with arousal) in the thalamus, results in lowered arousal which can range from lethargy (tiredness) to coma.

~

Aphasia is a language disorder or impairment that is apparent in reading, writing and speech, and is caused by injury to brain areas that specialise in these functions (usually this brain injury is due to stroke).

Aphasia:-

Broca’s aphasia Non fluent aphasia (language is not fluently expressed but speech is understood)

Wernicke’s aphasia Fluent aphasia (language is fluent and grammatically correct but doesn’t make sense; like a “word salad”)

Broca’s aphasia

Affects the left frontal lobe [where Broca’s area is located] The patient is aware of their condition They can fully understand speech, but cannot produce fluent speech themselves “girl ate the cake” … “cake was eaten by the girl” Broca’s aphasia’s patients get

confused!

Wernicke’s aphasia

Affects the left temporal lobe [where Wernicke’s area is located] The patient has little or no conscious awareness of their condition Speech can be fluently spoken and produced, but nothing they say makes sense! Although there is damage to the left hemisphere, some people with Wernicke’s aphasia

can still sing without any problems or use swear words and other emotionally charged language as normal

Spatial neglect

Spatial Neglect is an attentional disorder in which individuals fail to notice anything on either their left or right side. Specifically, they tend to behave as though one side of their world does not exist.

Spatial neglect is most commonly observed in stroke and accident victims, who have damage to their rear area of the parietal lobe in their right hemisphere – which means they neglect the left side of their world.

Although neglect is mostly experienced in the visual sense (people see only one side of an object, etc), spatial neglect can also occur for other senses, such as hearing, touch or movement.

Spatial neglect not only hinders our ability to see one side of external objects, it also applies for internal thoughts. For example, if you were to remember how a childhood toy looked like, you would see it in your ‘mind’s eye’ as having one side (left or right side of the toy would be missing)

The much greater occurrence of spatial neglect on the right parietal lobe (rather than the left parietal lobe), indicates the importance of the right parietal lobe and right hemisphere in both attention and conscious awareness of objects, both internally and externally.

One explanation of spatial neglect proposes that spatial neglect may be caused by failure of cortical arousal associated with the activities of the thalamus and reticular activating system.

Split-Brain Studies

Split-Brain studies involve studying the effects of “splitting the brain” ; that is, severing the corpus callosum which acts as a bridge for information to transfer between the two hemipsheres

Specifically, split-brain surgery involves surgically cutting the corpus callosum (and any other nerves that connect the two hemispheres), thereby disconnecting one hemisphere from the other. The effect of this is that the two hemispheres cannot receive information from each other anymore.

Split-Brain surgery is an invasive method (physically interferes with the brain) and is undertaken as a “last resort” to help people suffering from epilepsy, by preventing the spread of severe epileptic seizures from one side of the brain to the other.

Split-brain patients do not seem to have any major side effects as a result of their surgery, despite the fact that, after the operation, the two hemispheres virtually act as two independent brains. The patient’s personality & behaviour, after the operation, in most cases appears normal. 1950’s split brain studies with cats – Sperry and Myers Meyers and Sperry showed that when the cat had its optic chiasm (part of the brain where the optic nerves partially cross) and corpus callosum cut, two independent learning centres were established - one in each hemisphere of the cat's brain. If the cat had its right eye open and its left eye covered and learned to make a simple conditioned response (such as pressing a lever), it was unable to make the same response when the right eye was covered and the left eye was open. It was as if the learning was unable to be communicated to the other side of the brain; thus, it was obvious that information available to one side remained off-limits to the other; and also that cutting the corpus callosum did not allow information going into one hemisphere from reaching the other. Sperry concluded that the brain had, "Two separate realms of conscious awareness; two sensing, perceiving, thinking and remembering systems." Bogen and Vogel – first performed spilt-brain surgery on patients, ensuring not to repeat previous mistakes: by ensuring that the surgical disconnection of the two hemispheres was COMPLETE; that the corpus callosum and ALL nerves connecting the two hemispheres were cut. This procedure was successful and many patients were seizure-free afterwards with minimal side effects.

Sperry makes a comeback with his student Gazzaniga Sperry and his student Gazzaniga, designed a series of experiments to test Bogen and Vogel’s split-brain patients. Sperry’s aim was to understand the effects of disconnecting one hemisphere from the other, and to thereby address the question of how hemispheres work in a “normal” brain.

So why is the patient unable to identify images flashed in the LEFT visual field? If the visual information sent to the right hemisphere cannot cross back to the left hemisphere (because the corpus callosum has been cut), the patient would not be able to say what they saw. Although they can see the image, they can’t say what the speak to say what the image is, as the left hemisphere controls speech. Thus, Sperry’s findings not only provided research evidence about the specialised functions of the two hemispheres, but it also determined the role of the corpus callosum in the exchanging of information between the two hemispheres. Sperry believed that: CONSCIOUSNESS = combined result of both hemispheres in the intact brain

With the corpus callosum gone, why aren’t the hemispheres in continuous conflict, each providing a different conscious experience of the world?

The two hemispheres of the brain can compensate for the absence of the corpus callosum and can still coordinate their activities. Any one particular function is NOT exclusively performed only by one hemisphere

Not all nerve fibres are completely cut during split-brain surgery. Lower areas remain intact, for some motor and sensory information to be exchanged between hemispheres via these nerve fibres.

Each hemisphere learns to communicate with the other, by observing and responding to the mental processes or behaviour that the other produces. E.g. the right hemisphere may perceive something unpleasant and trigger a frown, which the left hemisphere may observe and respond to by saying “I’m displeased”.

Perceptual anomalies

Perception occurs when sensory information reaching the brain is meaningfully interpreted.

Perceptual anomaly refers to an irregularity in perception. It usually involves a mismatch or inconsistency between the perceptual experience and actual reality. Example: visual illusions

Motion after effect is the apparent movement of a stationary stimulus (object) following the extended viewing of a continuously moving stimulus (object). The stationary stimulus appears to move in the opposite direction.

Studies indicate that eye movements and neurons in the visual cortex (that are specialised to detect and respond to motion) are both involved in the illusory effect of MAE. Studies have also found that there are neurons in the visual systems that are sensitive to the direction of movement. In humans, these neurons are located in the retina and the visual cortex at the back of the brain. Prolonged exposure to a particular direction of movement (say, downwards) can “fatigue” and therefore reduce the responsiveness of the neurons preferring downward movement; while neurons sensitive to upward motion maintain their normal level of activity (as they are not sensitive to downward movement so they keep going), thereby producing the motion after effect. The MAE is believed to occur until the “fatigued” neurons have recovered. MAE’s can also provide insights into the visual systems of people whose brains are not functioning correctly, such as those who have Parkinson’s disease, schizophrenia, epilepsy and migraines.

Change Blindness refers to the difficulty observers have in noticing large changes to visual scenes. Change blindness occurs when the change is both expected and unexpected.

When change is expected we may eventually detect the change; but may take very long to do so

For example: two photos of real world objects that are almost identical are shown. The original and modified scenes are presented using a flicker technique. This involves presenting the original scene and the modified scene one after the other repeatedly, briefly separated (80 milliseconds) by a blank screen after presentation. The observers are then asked to search for the changing aspect of the picture every time the flicker occurs. Observers eventually identify the changes, but they take a very long time in doing so.

For change blindness to occur, the change in the scene has to occur during some kind of visual obstruction, such as movement of the eyes. This means that change blindness is different from

inattentional blindness. Inaattentional blindness is a failure to notice something in a scene when the scene remains continually in sight.

Change Blindness requires the presence of a visual disruption and requires comparison of one image to another (both of which are held in Short term memory)

Inattentional Blindness does not require a visual disruption (as the scene being observed remains continually in sight and does to rely on memory)

In 1998, Ronald Rensink used the “flicker technique” to test whether people could

consciously “sense” a change even if they had no visual experience of the change (i.e. they could not actually see the change). Observers pressed a button first when they “sensed” that something was changing (t1) and then they pressed it once again when they “visually experienced” the change. 14 out of 40 (25%) of observers reported “feeling and sensing” as though something was changing in a large number of trials.

According to Rensink, the results of this study suggest that some people have an already

limited ability to detect changes in a scene, even when they have no conscious experience (sense a change) of it. Also, some people can have a conscious experience of a change (sense a change) without actually seeing the change visually.

Change Blindness studies make it clear, that although focused attention is

needed to detect changes in a visual scene, focused attention alone does not guarantee that we will detect the change, even if the change is large, expected and should be easily noticed.

Although we must look in order to see, the findings of change blindness studies suggest that just looking is not enough. For example, if you were to turn your head and look into a tree because you heard a bird chirping, you will often fail to see the bird straightaway, and it will take you some effort before you actually see the bird. Similarly, a person whose mind wanders off during driving will often miss important road signs, even when these road signs are large and highly visible. In both situations, something prevents the observer from using their perceptual information (needed for perception) to see the new objects that have entered their field of vision. One explanation for this is that simple focused attention might not be enough; and that other cognitive processes must accompany attention in order for us to perceive a change in a visual scene

In order to perceive change in our visual world, we must:

Focus attention on the scene Form a visual mental representation of the scene (for example; as an icon) Store this in our ‘visual memory’ (so we can compare the two images in our brain to see

if there’s any change)

Synesthesia is a perceptual experience in which stimulation of one sense produces additional and unusual experiences in another sense.

For synesthetes (people with Synesthesia), the senses become intertwined and mixed up instead of remaining separate

Synesthesia is:

Involuntary ; occurs automatically when a certain sense is stimulated Extremely difficult to suppress The experience is vivid, highly memorable and consistent across time (for e.g. The

synesthetes always associates the same colour with the same number or alphabet) Synesthesia tends to be one-way; a sound may produce a taste but a taste may not

produce a sound

It has been found that there may be unusual brain processes associated with Synesthesia. Also, there may be a genetic link to the condition

Synesthesia is relatively rare, and there are individual differences in how different people experience it

It’s most accurate estimate for prevalence is 1 in 2000 people

Researchers still know very little about Synesthesia. However this much is understood:

Some researchers have suggested that synesthetes may be unusually sensitive to external stimuli

Others say that Synesthesia is a result of the breakdown of sensory and perceptual processes

It has also been suggested that Synesthesia may be linked to the excess of neural connections

Many psychologists believe that the brain of synesthetes has unique structural/functional properties; that synesthetes may have abnormal nerve pathways or be “wired differently” so that sensory areas in the brain cross-activate each other, thereby triggering additional and unusual sensations

Synesthesia is not associated with any serious brain abnormalities, nor is it some kind of sixth sense

Brain Research Methods

Although early brain research provided significant information about the structure of the brain, very little was known about the function of the brain. For example: how different brain structures work, their relationships to other brain structures/areas and the neural pathways connecting them.

Neuroimaging is brain imaging that can capture detailed images of the living intact brain as it engages in behaviour and mental processes. There are two types of neuroimaging or brain imaging techniques:

Structural neuroimaging: shows brain structure and anatomy (e.g. CT Scans and standard MRI scans)

Functional neuroimaging: shows aspects of brain function by showing the brain “at work” (e.g. PET, SPECT and fMRI)

DIRECT BRAIN STIMULATION

Involves using an electrode to apply a weak electrical current (usually in the form of short pulses that mimic neural impulses) to stimulate particular parts of the brain

Assumption: If Direct Brain Stimulation stimulates a response in a certain brain area, then that area of the brain controls and is responsible for that particular response For example: The stimulation of the movement of a particular body part may be associated with the stimulation of a certain brain area

Direct brain stimulation may also impair the functioning of a specific brain area, thereby also impairing the response associated with that brain area For example: a person’s speech may stop mid-sentence while they are talking. However, this disruptive effect is only apparent when the person is actively engaged in the behaviour that the direct brain stimulation impairs or prevents. Furthermore, this disruption that causes impaired functioning that leads to an impaired response is most evident in complex functions such as language and memory

In the 1940’s , Wilder Penfield used Direct Brain Stimulation to identify and locate areas of the cerebral cortex which were responsible for functions such as movement and touch. He stimulated particular brain areas and asked patients to report on the result. Using this technique, he enabled the “mapping of brain areas”

ADVANTAGES OF DIRECT BRAIN STIMULATION

A way of investigating the function of living brain areas Has enabled researchers to locate various brain structures and determine their

functions; provides evidence for hemispheric specialisation Allows us to study localised motor and sensory functions Able to highlight the function of inactivated regions Direct Brain stimulation gives relief of symptoms to patients who have either difficulty

taking particular medication or who have not responded to medication (especially helpful for people with Epilepsy, Tourette’s syndrome, Phantom limb pain, Obsessive compulsive disorder, major depression, and Parkinson’s disease)

Direct Brain Stimulation helps to identify the function of different areas of the brain; provides evidence for hemispheric specialisation for functions such as language

DISADVANTAGES/LIMITATIONS OF DIRECT BRAIN STIMULATION

Invasive; because Direct brain stimulation requires either surgery or injections into the brain as part of the process – thus, poses unacceptable risks to the patient

As Direct brain stimulation patients don’t have normal brains to begin with, it is difficult to generalise the results of their brain stimulation to the rest of the normal population

Research based only on clinical patients (only those undergoing brain surgery) Crude; it is not easy to tell how far the stimulation has spread

Transcranial Magnetic Stimulation (TMS)

Transcranial magnetic stimulation involves using a handheld coil to deliver a magnetic field pulse through the skull, which allows researchers to either activate or stop activity in a specific area of the brain

The magnetic field pulse that is transmitted from a small copper electromagnetic coil that is enclosed in plastic and placed next to the scalp

This coil creates a magnetic field that can penetrate the brain to a depth of 2 cm. This means that the coil does not penetrate deeply, and it only affects the part of the brain that lies immediately below the skull (it doesn’t affect the whole brain)

The magnetic pulses can vary according to time and duration with the capacity to

either increase or decrease the activation of neurons (and activity of brain) in the targeted area

A brief single pulse sent through the skull can cause a burst of brain activity.

For example; when the coil is placed just above the skull over an area of visual cortex in the occipital lobe, the participant usually detects or sees flashes of light

If the coil is placed over an area of the motor cortex in the frontal lobe, the patient may experience a brief muscle twitch somewhere in the body

When TMS is used in the delivery of a single pulse through the skull Single Pulse or Non-Repetitive TMS

When TMS is used in the delivery of a repeated pulse through the skull Repetitive TMS (rTMS)

ADVANTAGES OF TMS

o TMS is a non-invasive technique. o Can be used with healthy AND clinical participants o Provides a way to investigate the function of living brain areas o Can highlight the function of inactivated regions of the cerebral cortex o Can demonstrate the role of brain regions or areas in the performance of specific tasks o It is very good at either stimulating or deactivating specific areas of the brain to

determine the function of that area; thus allows mapping brain function o Relatively inexpensive – cost effective

DISADVANTAGES/LIMITATIONS OF TMS

o As it sends an electrical current through the brain, TMS can cause a seizure. This is of particular concern for patients with epilepsy or patients who are on medication.

o The stimulation of the scalp causes some discomfort and pain o Very poor spatial resolution – as the coil does not reach far below the scalp o Because the coil is hand-held, it is hard to control the target site o Cannot be used near other scanners (interference)

BRAIN RECORDING AND IMAGING TECHNIQUES

Electroencephalograph (EEG)

The Electroencephalograph (EEG) is a device that detects, amplifies and records the electrical activity generated by the brain

A series of electrodes are attached to the scalp and the activity of neurons near each electrode is recorded, amplified and transferred onto paper as wavelike patterns

Changes in electrical activity of the brain are evident in sleep, arousal, wakefulness, epilepsy and coma

ADVANTAGES OF EEG

o Provides useful general information about the brain without being invasive o Non-invasive and safe o EEG equipment is less expensive and more readily available to the researcher o Can be used to study brainwave activity over long periods of time, such as in the study of sleep

o Can be used for research with Healthy AND Clinical participants

DISADVANTAGES/LIMITATIONS OF EEG

o Time consuming process o Averaging the activity from millions of neurons does not provide specific information

about the function of brain structures that have been activated o Only maps the surface of the cortex o Not an imaging technique – does not provide images of the brain o Unpredictable

Computerised Tomography (CT)

Computerised Tomography (CT) is when a series of X-rays are sent through a patient’s head at different angles, producing information that a computer then builds into detailed cross sectional images of the brain that show the structure of the brain, but not its function.

Before the X-rays are taken, the patient is injected with an iodine based substance known as ‘contrast’; which highlights blood vessels in the brain; allowing for easier interpretation and reading of the CT image

The X-ray scanner that moves around the patient’s head emits some radiation

The cross sectional images of the brain are 2-D, but can be combined to produce the 3-D representation of the brain that is shown on the computer screen

Advantages of CT

o Provides detailed images that show the structure of the living brain o Can be used for research with Healthy AND Clinical participants o Allows for observation of physical differences in brains of patients with Alzheimer’s

disease, Parkinson’s disease and Schizophrenia o Brain damage and neural abnormalities can be clearly detected; e.g. Brain Tumours o Adjacent slices of the brain can be combined to form 3D representation of the brain

Disadvantages of CT

o No information regarding function of the brain o Expensive technique o Requires highly trained staff o CT’s use X-rays; and because X-rays have potential health risks, frequent use of CT is

not recommended o Poor localisation

Positron Emission Tomography (PET)

Positron Emission Tomography (PET) is when a computer produces computer generated image that gives information about brain function and activity during the performance of tasks by tracking blood-glucose levels with a radioactive tracer after radioactive glucose or oxygen compounds are injected into the bloodstream.

It is called “Positron Emission” because the radioactive compound (that was injected) gives out or emits positrons (minute particles with positive charge); a Radiation Detector Camera determines from which areas of the brain these positrons are emitted

The pictures that PET produces are colour coded according to level of brain activity: Red signifies the highest level of neural activity, whereas violet signifies the lowest level of neural activity

ADVANTAGES OF PET

o Provides detailed images that show the function of the brain o Can be used for research with Healthy AND Clinical participants o Can potentially image the whole brain o Moderate to high spatial resolution o Colour coding in PET scans make the images easier to read and interpret o PET is useful for locating brain abnormalities and brain damage; e.g. a tumour would be

seen as a “very active” area on the scan

DISADVANTAGES/LIMITATIONS OF PET

o Mildly invasive – because of injection of radioactive compounds o Use of radioactive compounds – means only a limited number of scans can be performed

on a single patient o PET images do not provide clear structural information of the brain o Very poor temporal resolution o Very expensive o Requires highly trained radiography staff o Sedation may be necessary for the patient to lie still for the scan

SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY (SPECT)

Single Photon Emission Computed Tomography (SPECT) is a variation of PET that uses a longer lasting radioactive tracer and scanner to record data that the computer uses to generate 2D and 3D functional images of active brain areas.

The main aim of SPECT imaging is to measure the blood flow of a certain brain area by mapping the distribution of injected radioactive compounds in the brain

ADVANTAGES OF SPECT

o Cheaper to run and more accessible than PET o Can be used for research with Healthy AND Clinical patients o Provides 3D imaging of different areas of the brain o Provides information about neuronal activity (like blood flow in certain regions of the brain)

DISADVANTAGES/LIMITATIONS OF SPECT

o Mildly invasive; because of the injection of radioactive compounds o Use of radioactive material – means that only a limited number of scans can be

performed on a single patient o Limited spatial resolution – Less clear and detailed than PET o Scans with SPECT take longer to complete

Magnetic Resonance Imaging (MRI)

Magnetic Resonance Imaging (MRI) uses harmless magnetic fields and radio-waves to vibrate atoms in the brain’s neurons, thereby producing a computer generated image of the brain that shows high and low levels of brainwave activity.

The patient must sit motionless in a chamber (that is like a large electromagnet) and they are exposed to short powerful bursts of magnetic fields

These magnetic fields stimulate protons in the brain’s tissue to emit radio signals; which are picked up by the computer and analysed to form an anatomical image of a “slice” of the patient’s brain

The MRI is especially useful as it provides greater contrast between Normal and Abnormal tissue White and grey matter

MRI also produces frontal and sagittal (side view) images of the brain

Advantages of MRI

o Provides very detailed knowledge about structure of the brain o 3D Imaging of the brain o Non-Invasive; Painless; Safe o Can be used for research with Healthy and Clinical participants o MRI can be used to find structural abnormalities in the brain. E.g. MRI can detect

the difference between a cancerous cell and a non-cancerous cell o MRI provides more clear and detailed structural images than CT

Disadvantages/Limitations of MRI

o Very expensive o Not as commonly available as the CT o MRI does not provide information about function of the brain o Sedation may be necessary – as the chamber may be claustrophobic for some people o Cannot be used with people who have metal in their bodies like steel pins,

pacemakers o MRI is susceptible to transient scanner effects, and artefacts (‘ghosting’) due to head movement

Functional Magnetic Resonance Imaging (fMRI)

Functional Magnetic Resonance Imaging (fMRI) is an application of MRI that shows brain areas that are active during performance of tasks by detecting changes in oxygen levels used by neurons in the brain.

fMRI, like the standard MRI, also uses harmless magnetic fields and radio-waves to produce a computer generated image of the brain

In addition, however, fMRI monitors blood flow and oxygen consumption to reveal areas of the brain that display greater brain activity- and therefore greater brain function.

In an fMRI experiment:

Subjects are required to carry out a cognitive task and the fMRI device produces an image every second to highlight the locations of the brain and the levels of activation at these locations

This allows the researcher to actively and accurately monitor which brain regions become active and for how long they are active

ADVANTAGES OF fMRI

o Non-invasive and Non-toxic o fMRI is widely available and cheaper than PET o Provides clear images of brain functioning as different tasks are performed o Provides for 3D imaging of active brain areas o Can be used for research with Healthy AND Clinical participants o Excellent spatial resolution o fMRI images are taken as changes in the brain occur o Can also provide detailed images of brain structure

DISADVANTAGES/LIMITATIONS OF fMRI

o fMRI is a very expensive procedure o Not subject friendly; loud, claustrophobic, no metal items allowed o Sedation may be necessary; the chamber can be claustrophobic for some people o Susceptible to artefacts (ghosting) and transient scanner effects o Poor temporal resolution o Can’t be used with people who have metal in their bodies; like steel pins