IHTT

1

The Effect of Physiological Arousal on

Interhemispheric Transmission Time

Cathy Gouchie

Algoma University

Running Head: INTERHEMISPHERIC TRANSMISSION TIME

IHTT

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The Effect of Physiological Arousal on

Interhemispheric Transmission Time

The rate at which information can be transmitted

between cerebral hemispheres may change, depending on

the circumstances. An increase in physiological

arousal may increase interhemispheric transmission

time (IHTT), the time taken for information to cross

from one hemisphere to the other. A brief review of

relevant neuroscientific facts and some previous IHTT

research will provide a better understanding of this

hypothesis.

Cerebral Hemispheres

The cerebrum of the human brain is divided into

two physically similar cerebral hemispheres. The

functions of the hemispheres are not symmetrical as

their appearance might indicate. In right handed

people, most language functions are concentrated in

the left hemisphere (including Broca's and Wernicke's

areas), though emotional inflection is provided by

the right hemisphere. The right hemisphere is

superior in recognizing faces, and in visual-spatial

and melodic skills. According to Segalowitz (1983)

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the right hemisphere seems to be necessary for

integrating information and making inferences from

that synthesis.

In general, the left side of the body is

controlled by the motor cortex in the right half of

the brain and vice versa. Although uncrossed motor

pathways are known to exist, movement of the

individual limbs, especially their distal parts, are

the concern of the crossed pathways (Keypers, cited

in DiStefano, Morelli, Marzi, and Berlucchi, 1980).

Also some sensory information from one side of the

body is carried to the opposite hemisphere.

Visual reception is also crossed in the brain.

The optic fibers are partially crossed at the optic

chiasm. Because of this, all information projected

from the left visual field (to the left of a point

where both eyes are focused), is transmitted to the

right hemisphere. Information from the right visual

field is transmitted to the left hemisphere.

If the two sides of the brain were not able to

communicate, each would receive different visual

images and different sets of information from the

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environment. This is not the case since the

hemispheres are joined together by several bundles of

connecting fibers, the largest of which is the corpus

callosum. Normally, all information received by one

hemisphere is shared with the other hemisphere via

the corpus callosum. In this way, visual information

is integrated and only one image is seen.

Neural Transmission

The electrical nature of neural transmission

involves ions. At rest, the inside of a neuron

maintains a negative charge, due to an excess of

negative ions, with respect to the outside which

contains more positive ions. This resting potential

must be altered for a message to be transmitted. If

the change in potential is large enough, it passes a

threshold and an action potential is triggered. This

causes a sudden change in the permeability of the

cell membrane, allowing an influx of positive ions.

This change, the nerve impulse, spreads down the

length of the nerve fiber until it reaches a synapse.

The electrical charge in the fiber then returns to

normal.

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Each presynaptic terminal measures, in some way,

the number of signals arriving as electrical

impulses. When a sufficient number has arrived, the

terminal releases a neurotransmitter into the

synapse. This chemical crosses the synapse to

specialized receptors on the postsynaptic membrane of

the next neuron. Each receptor is specialized in

that it accepts only one of the many

neurotransmitters (Thompson, 1985).

Some neurotransmitters are excitatory and

increase the likelihood that a nerve impulse will be

created, while others are inhibitory and reduce the

chances of impulse firing. The rate at which a nerve

fires depends on the number and type of signals it

receives. The firing rate will increase if the

neuron receives many excitatory signals together; if

it receives many inhibitory signals, the firing rate

tends to decrease (Bootzin, Bower, Zajonc and Hall,

1986). The more rapidly a neuron fires, the more

neurotransmitters are released, therefore the greater

the effect on the receiving neuron.

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Through special techniques, locations of

specific neurotransmitter receptors in the brain have

been identified. For example, in a study of the

monkey brain by Snyder (1975, cited in Bignami and

Michalek, 1978), the highest density of acetylcholine

(ACh) receptors was found in the putamen, a part of

the basal ganglia. The lowest density was in the

optic chiasm, with fairly high levels present in

various areas of the cerebral cortex, thalamus and

hypothalamus, and a lower density in the corpus

callosum. However, as noted by Siggins and Bloom

(1981), most circuits of the cerebral cortex and

their neurotransmitters remain to be determined.

Alteration of neurotransmitter activity due to stress

Barry and Buckley (cited in Anisman, 1978)

described stress as stimulation that requires

behavioural and/or physiological adjustments. The

stimulation usually, but not always, represents a

threat to the animal's well-being. One effect of

stress is the arousal of the sympathetic nervous

system, leading to physiological change such as

increased heart rate, deeper and more rapid

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breathing, and a decrease in the galvanic skin

response. These changes mobilize the body for action

so the stressor can be better managed. This is

inferred by the Yerkes-Dodson Law, which says that

higher levels of arousal tend to improve performance

for tasks that are simple, or which require little

cognitive involvement. The more difficult the task,

the more it may be disrupted by high levels of

arousal.

Another consistent physiological change present

during stress is alteration in neurotransmitter

activity, including norepinephrine, dopamine,

acetylcholine and serotonin (Anisman, 1978). Several

factors, listed by Anisman, determine the extent of

these changes. Included are the severity of the

stressor, predictability of stress onset, and control

over stress onset or termination. Most stressors

examined in the studies reviewed by Anisman led to

changes in neuronal activity.

The information reviewed so far in this paper

suggests the following line of reasoning. A stressor

produces physiological arousal, including alterations

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in neurotransmitter activity, designed to manage the

stressor and increase survival of the organism. In

man and many other animals, motor control and

reception of sensory information for one side of the

body is primarily the concern of the opposite, or

contralateral, hemisphere of the cortex. Also, many

brain functions are lateralized to one hemisphere.

An decrease in IHTT, possibly due to changes in

neurotransmitter activity or rate of nerve firing,

would allow faster integration of vital information.

This would offer a distinct advantage to an

organism's survival under stressful situations.

Producing Physiological Arousal

As previously mentioned, physiological arousal

produces changes in neurotransmitter activity.

Physiological arousal can be induced in experimental

subjects by submitting them to loud (approximately 90

dB) white noise. The noise should be presented

continuously since, if bursts of intermittent noise

are not generated by the person himself, it may

distract him from what he is doing (Poulton, 1979).

Poulton stated that continuous noise can have

IHTT

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different effects, depending on the nature of the

task. The increase in arousal, which accompanies

continuous noise, leads to improvement on simple

speed or vigilance tasks that respond well to

arousal. He pointed out that, while continuous noise

by itself does not appear to increase physiological

arousal for prolonged periods, having to perform a

challenging task in continuous noise may increase

arousal more than performing the task in quiet.

Measurement of IHTT

Most behavioural measures of interhemispheric

transmission time are based on reasoning originally

proposed by Poffenberger (1912, cited in Bashore,

1981). Simple reaction times (SRT) are measured in

response to a stimulus presented to one visual field

at a time. A stimulus presented to the right visual

field (RVF) is transmitted to the left hemisphere.

If a right-hand response (ipsilateral response) is

requested, the reaction time should be faster than if

the stimulus was presented to the left visual field

(LVF) and carried to the right hemisphere. In this

case, the information would have to be first

IHTT

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transferred to the left hemisphere before a right-

hand response (contralateral response) could occur.

The difference in reaction times is assumed to be the

time required for the information to cross to the

other hemisphere (interhemispheric transmission

time).

Several factors have been proposed to account

for the difference in reaction times between

ipsilateral and contralateral responses. As a result

of his study, Wallace (1971) stated that the response

times were dependent on spatial compatibility of the

stimulus and response hand. He requested subjects to

cross their hands (crossed position) in half the

trials and found that reaction times were fastest

when the stimulus and response hand were on the same

side, regardless of whether the response was

ipsilateral or contralateral. He used a choice-

reaction time procedure, however, where one stimulus

requested a right-hand response, and a different

stimulus requested a left-hand response. This is a

different, more complex task than that of the simple

reaction time experiments. According to Bashore

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(1981), it is reasonable to assume a correspondence

amoung task complexity, cerebral activation and the

amount of information that must be conveyed between

the two hemispheres.

Berlucchi, Crea, DiStephano and Tassinari (1977)

conducted a similar study but used a simple reaction

time paradigm. In addition to the normal

presentation of the stimulus, a stimulus was

presented at three different visual angles for each

subject. The results showed that the advantage of

ipsilateral responses over contralateral responses

was consistent. This was true whether the hands were

in the correct anatomical position or in the crossed

position. They concluded that the time of difference

between ipsilateral and contralateral responses is

best attributed to a difference in the anatomy of the

neural pathways involved in the two kinds of

responses. Ipsilateral responses are integrated

within one cerebral hemisphere and contralateral

responses require interhemispheric cooperation.

Berlucchi and his fellow workers (1977) also

found that ipsilateral responses were faster than

IHTT

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contralateral responses in both visual fields and for

all stimulus positions. This is in agreement with

the results of Berlucchi, Heron, Hyman, Rizzolatti

and Umilta (1971), where the delay between

ipsilateral and contralateral responses remained

constant regardless of the degree of eccentricity of

the visual stimuli.

Bashore (1981), after reviewing these many other

studies of IHTT, feels that sufficient research has

been done using SRT procedures to demonstrate

reliable estimates of IHTT. The average estimate of

IHTT using the SRT paradigm is approximately 3.0

msec.

Summary

If physiological arousal does cause a decrease

in IHTT, this change might be measured using a SRT

experiment. A noise of 90 dB, presented to some

subjects during the experiment, should induce

sufficient physiological arousal to allow any IHTT

differences to be measured.

IHTT

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References

Anisman, H. (1978). Neurochemical changes elicited

by stress. In H. Anisman and G. Bignami (Eds.).

Psychopharmacology of aversively motivated

behaviour (pp. 119-161). New York: Plenum Press.

Bashore, T. (1981). Vocal and manual reaction time

estimates of interhemispheric transmission time.

Psychological Bulletin, 89, 352-368.

Berlucchi, G., Crea, F., DiStefano, M. and

Tassinari, G. (1977). Influence of spatial

stimulus response compatibility on

reaction time of ipsilateral and contralateral

hand to lateralized light stimuli. Journal of

Experimental Psychology, 3, 505-517.

Berlucchi, G., Heron, W., Hyman, R., Rizzolatti,

and Umilta, C. (1971). Simple reaction times of

ipsilateral and contralateral hand to

lateralized visual stimuli. Brain, 94, 419-430.

IHTT

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Bignami, G. and Michalek, H. (1978). Cholinergic

mechanisms and aversively motivated behaviours.

In H. Anisman and G. Bignami (Eds.).

Psychopharmacoloqy of aversively motivated

behaviour (pp. 173-255). New York: Plenum Press.

Bootzin, R., Bower, G., Zajonc, R. and Hall, E.

(1986). Psychology today: An introduction. New

York: Random House.

DiStefano, M., Morelli, M., Marzi, C.A. and

Berlucchi, G. (1980). Hemispheric control of

unilateral and bilateral movements of proximal

and distal parts of the arm as inferred from

simple reaction time to lateralized light

stimuli in man. Experimental Brain Research, 38,

197-204.

Poulton,C. (1979). Composite model for human

perfo Rance in continuous noise. Psychological

Review, 86, 361-375.

Thompson, R.F. (1985). The brain. New York: W.H.

Freeman.

Segalowitz, S.J. (1983). Two sides of the brain.

New Jersey: Prentice-Hall.

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Siggins, G. and Bloom, F. (1981). Modulation of

unit activity by chemically coded neurons. In 0.

Pompeiano and C. Marsan (Eds.). Brain mechanisms

and perceptual awareness. (pp. 431-447). New

York: Raven Press.

Wallace, R.J. (1971). S-R compatibility and the

idea of a response code. Journal of Experimental

Psychology, 88, 354-360.

The Effect of Physiological Arousal on

Interhemispheric Transmission Time

Cathy Gouchie

Algoma University

IH1 1

Running Head: INTERHEMISPHERIC TRANSMISSION TIME

Abstract

The effect of physiological arousal on interhemispheric transmission

time (IH1 1') was investigated. Since physiological arousal produces

changes in neurotransmitter activity, these changes could result in a

decrease in IH1 1. IHTT was measured with a simple reaction time

(SRT) experiment using an IBM PC model 80 computer and customized

software. Physiological arousal was produced in 24 subjects through the

presentation of a loud (90 dB) white noise. Twelve were not submitted

to the noise. The results were inconclusive due to inaccurate

measurements of IHI'l . A possible reason for these results could be

the location of the stimulus. The light flash presented to subjects to

stimulate a response may have been situated too close to the centre of

the subject's field of vision rather than in the left or right visual fields.

IH 1 1

The Effect of Physiological Arousal on

Interhemispheric Transmission Time

Though the left and right cerebral hemispheres appear physically

similar, there are considerable and well-documented differences in their

functions (Segalowitz, 1983). Tactile and visual information is

transmitted directly to the hemisphere opposite to the side of the body

that received the information. Motor control of the limbs also rests

within the hemisphere on the opposite side of the body.

The hemispheres are joined together by several bundles of

connecting fibers, the largest of which is the corpus callosum Any

advantage gained by one hemisphere through lateralization of function,

or any sensory information coming into only one hemisphere, is shared

with the other hemisphere by transmitting information across the corpus

callosum

The rate at which information can be transmitted between cerebral

hemispheres may change, depending on the circumstances. An increase

in physiological arousal may decrease the interhemispheric transmission

time (IH I 1'), the time taken for information to cross from one

IH I I

hemisphere to the other. Vital information could therefore be

integrated more quickly, offering a distinct advantage to an organism's

survival under stressful situations.

IH I I can be measured using a simple reaction time (SRT)

experiment. This paradigm is based on reasoning originally proposed by

Poffenberger (1912, cited in Bashore, 1981). Simple reaction times are

measured in response to a stimulus presented to only one visual field at

a time. A stimulus presented to the right visual field (RVF) is

transmitted to the left hemisphere. If a right hand response (ipsilateral

response) is requested, the reaction time should be faster than if the

stimulus were presented to the left visual field (LVF) and carried to the

right hemisphere. In this case, the information would have to be first

transferred to the left hemisphere before a right hand response could

occur (contralateral response). The difference in reaction times is

assumed to be the time required for the information to cross to the

other hemisphere (interhemispheric transmission time-IHTT).

Several behavioral studies have been performed on measurements of

IHTT. After reviewing many of these studies of IHTT, Bashore (1981)

felt that sufficient research had been done using SRT procedures to

IHI I

demonstrate reliable estimates of IH'I 1. The average estimate is

appc,..,.(imately 3.0 insec.

Based on previous am research, it should be possible to comparedifferences in IHTT under different conditions using the SRT paradigm.

If physiological arousal can be induced in some subjects, a decrease in

IHTT compared to subjects under normal conditions may be detected.

Method

Subjects

Thirty-six psychology students (eight male, twenty-eight female) at

Algoma University took part in this study on a voluntary basis. They

were all right-handed, with normal or corrected vision as tested on the

Lomb Orthorater. They ranged in age from 18 to 45 years.

,,:„Jed for their participation with bonus marks in one

of their psychology courses. All were treated in accordance with the

"Ethical Principles of Psychologists" (American Psychological

Association, 1981).

Procedure

was seated with the head positioned so a fixed viewing

distance of 17 cm from the computer screen was maintained. This

ensured that the stimulus was presented at the proper visual angle. The

IH11

ghL tad rested of the table with the index finger prepared to hold

down the response button. Subjects were instructed to focus on the

fixation point at all times, and to lift their finger from the button as

quickly as possible whenever a stimulus appeared, whether it was to the

left or right of the fixation point.

Stimuli were presented on the display screen of an IBM PC Model

30 computer utilizing customized software. A small fixation spot

remained present in the centre of the screen throughout the session.

Before each trial, the computer displayed written instructions to press

the button and hold it down when ready to proceed with the trial. Once

the button was pressed, and after a delay varying randomly between 500

and 1500 cosec (to discourage anticipatory responding), the stimulus

symbol was presented for 25 msec subtending 4 of visual angle to

either the left or right of the fixation point. The presentation and

randomization of the left-right trial sequence was controlled by

computer. Any reaction times (RT) that fell outside the range of 100-

1000 rnsec were excluded since very short RT may be due to

anticipation and long RT may be the result of lapse of attention (Milner

and Lines, 1982). Release of a microswitch attached to the computer

terminal served as the response. The time from onset of stimulus to

IH'I I

release of the button was measured and recorded by the computer as

the reaction time.

Each test session consisted of 20 practice trials, followed by 6 blocks of

40 trials each. There was a rest period of several minutes between each

block. All subjects were asked to wear earphones throughout the

experiment. Physiological arousal was produced in some of the subjects

by submitting them, through use of the earphones, to a loud (90 dB),

continuous white noise. Poulton (1979) pointed out that the increase in

arousal, which accompanies continuous noise, leads to improvement on

simple speed or vigilance tasks. Noise of 90 dB during the reaction time

experiment should, therefore, produce sufficient physiological arousal to

allow any IHTT advantages, derived from increased arousal, to be

measured. Twelve of the subjects (early noise group) were submitted to

the noise after completion of the second block. Another twelve (late

noise group) were submitted to the noise after the fourth block. The

final twelve served as a control group and wore the headphones but

were not exposed to the noise.

IL recorded every ten seconds during the practice and

experimental trials using a Inque pulse monitor model PU-701 and the

values were averaged for each block. During the interval between

IH11

blocks blood pressure was measured with a Copal digital

sphygmomanometer UA-271.

Results

The mean RVF response times were subtracted from the mean LVF

times to produce a measure of IHTT per block for each subject.

However, as Figure 1 shows, many of the IH I I values calculated in this

way were negative, a reversal of the expected results. Most

Insert Figure 1 about here

subjects produced both negative and positive values, indicating that the

times measured were not actually interhemispheric transmission times.

The effect of noise on the physiological arousal of the subjects can

be seen from Figure 2. Changes

Insert Figure 2 about here

in pulse rate, calculated by subtracting mean pulse rate/block from the

mean pulse rate for the practice trials, declined in the control group as

the experiment progressed. The same trend was observed in the late

9

noise group until the noise was introduced. At this point the heart rate

leveled off. Pulse rate in the early noise group remained relatively

constant throughout the experiment and higher than for all other groups.

Blood pressure did not change significantly during the experiment.

Discussion

Due to the invalid measurements of IH1 1', it cannot be determined

from this experiment whether or not physiological arousal increases the

rate that information is transmitted between hemispheres.

As predicted by Poulton, a continuous noise of 90 dB did increase

the physiological arousal in the experimental subjects. The task

required of the subjects was basically a long, eventually monotonous one

and, as indicated by the pulse rate of the control subjects, physiological

arousal decreased as the experiment proceeded. The late noise

experimental group also began to relax until the introduction of the

noise after the fourth block of trials. The pulse rate then ceased to

decline, remaining instead at the level it was before the noise was

activated. The pulse rate of the early noise group did not decline

indicating the subjects in this group did not relax, probably attributable

to the noise they were listening to.

IH1T

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Figure 3 illustrates the results expected from this study if

physiological arousal does increase IHTT. Since the physiological

arousal level of the

Insert Figure 3 about here

control group decreases, the time it takes for a message to cross from

one hemisphere to the other may take slightly longer. The late noise

group would also show an increased IH I at the beginning since

physiological arousal in that group also decreased at the beginning of

the experiment. The early noise group would be expected to have fairly

constant measurements of IH'1 1 since their level of arousal remained

relatively constant throughout the experiment.

re vresearch on IHTT using the simple reaction time paradigm

produced reliable measurements of around 3 msec (Bashore, 1981).

Milner and Lines (1982) also found consistent results measuring IHTT

with a simple reaction time paradigm using computers. Since the

current study was based on the theory and methodology of these

previous studies ( Berlucchi, Crea, DiStefano, and Tassinari, 1977;

Berlucchi, Heron, Hyman, Rizzolatti, and Umilta, 1971; DiStefano,

11

Morelli, Marzi and Berlucchi, 1980), the measurements of IH I I should

have been similar. However, many of the values were negative

indicating that for some reason the procedure did not measure IH I I as

intended. If negative values were consistently obtained, this would mean

that the contralateral response was faster for some reason. However,

positive and negative values were evenly mixed.

There is no explanation yet as to why the methods designed for use

in this study failed to measure IHTT. A possibility is that the stimuli

were not displayed at a great enough visual angle to ensure presentation

to only one visual field at a time If this is the case, it is an adjustment

easily made for replication of the experiment in the future.

IHTT

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References

American Psychological Association (1981). Ethical

principles of psychologists. American

Psychologist, 36, 633-638.

Bashore, T. (1981). Vocal and manual reaction time estimates of

interhemispheric transmission time. Psychological Bulletin, 89, 352-

368.

Berlucchi, G., Crea, F., DiStefano, M. and Tassinari, G. (1977).

Influence of spatial stimulus response compatibility on reaction time

of ipsilateral and contralateral hand to lateralized light stimuli.

Journal of Experimental Psychology, 3, 505-517.

Berlucchi, G., Heron, W., Hyman, R., Rizzolatti, and Umilta, C.

(1971). Simple reaction times of ipsilateral and contralateral

hand LO lateralized visual stimuli. Brain, 94, 419-430.

DiStefano, ivl., Morelli, M., Marzi, C.A. and Berlucchi, G.

(1980). Hemispheric control of unilateral and bilateral

movements of proximal and distal parts of the arm as inferred from

simple reaction time to lateralized light stimuli in man.

Experimental Brain Research, 38, 197-204.

IH' I I

13

Milner, A. and Lines, C. (1982). Interhemispheric

pathways in simple reaction time to lateralized

light flash. Neuropsychologia, 20, 171-179.

Poulton,C. (1979). Composite model for human performance in

continuous noise. Psychological Review, 86, 361-375.

Segalowitz, S.J. (1983). Two sides of the brain. New Jersey: Prentice-

Hall.

IH'I I

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Figure Caption

Figure 1. Mean IHTT measurements per block of trials.

Figure 2. Mean changes in pulse rate per block of trials.

Figure 3. Diagram of expected IH 1 1 measurements.

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