Memory Has Temporal Stages: Short, Intermediate, and Long

• Iconic memories are the briefest memories and store sensory impressions that only last a few seconds.

• Short-term memories (STMs) usually last only for up to 30 seconds or throughout rehearsal. – Short-term memory is also known as working memory.

• An intermediate-term memory (ITM) outlasts a STM, but is not permanent.

• Long-term memories (LTMs) last for days to years.– Long-term memory has a large capacity.

– Information can also be forgotten or recalled inaccurately.

Stages of Memory Formation

Memory Has Temporal Stages: Short, Intermediate, and Long

Working memory can be subdivided into three components, all supervised by an executive control module:

• Phonological loop—contains auditory information• Visuospatial sketch pad—holds visual impressions• Episodic buffer—contains more integrated, sensory

information

A functional memory system incorporates three aspects:• Encoding—sensory information is passed into short-term

memory.• Consolidation—short-term memory information is

transferred into long-term storage.• Retrieval—stored information is used.

Hypothesized Memory Processes: Encoding, Consolidation, and Retrieval

Memory Has Temporal Stages: Short, Intermediate, and Long

Mechanisms differ for STM and LTM storage but are similar across species.

• The primacy effect is the higher performance for items at the beginning of a list (LTM).

• The recency effect shows better performance for the items at the end of a list (STM).

Serial Position Curves from Immediate-Recall Experiments

Successive Processes Capture, Store, and Retrieve Information in the Brain

• Multiple brain regions are involved in encoding, as shown by fMRI.

• For recalling pictures, the right prefrontal cortex and parahippocampal cortex in both hemispheres are activated.

• For recalling words, the left prefrontal cortex and the left parahippocampal cortex are activated.

• Thus, the prefrontal cortex and parahippocampal cortex are important for consolidation.

• These mechanisms reflect hemispheric specializations(left hemisphere for language and right hemisphere for spatial ability).

Encoding, Consolidation, and Retrieval of Declarative Memories

Event-related fMRI studies of episodic encoding and retrievalJ. Spaniol et al. / Neuropsychologia 47 (2009) 1765–1779

Fig. 1. ALE maps thresholded at p < .05, corrected. Enc = encoding success; Ret = retrieval success. For the Enc vs. Ret difference map, areas more active for encoding than for retrieval are shown in green. Areas more active for retrieval than for encoding are shown in blue.

Successive Processes Capture, Store, and Retrieve Information in the Brain

• The process of retrieving information from LTM can cause memories to become unstable and susceptible to disruption or alteration.

• Reconsolidation is the return of a memory trace to stable long-term storage after it’s temporarily volatile during recall.• Reconsolidation can distort memories.

• Successive activations can deviate from original information.

• New information during recall can also influence the memory trace.

• Leading questions can lead to ‘remembering’ events that never happened.

• ‘Recovered memories’ and ‘guided imagery’ can have false information implanted into the recollection.

Role of the Hippocampus in Reconsolidation

• Damage to the hippocampus– can produce Anterograde amnesia

– as in the case of H.M.

– can not consolidate new information

• What role does the Hippocampus play in LTM?– LTM is not stored in hippocampus

– Hippocampus may be needed for retrieval of “recent” LTM whereas “older” LTM is only processed by cortex

– Reconsolidation concept implies that LTM is processed through hippocampal circuits i.e. working memory

– Frequent? Or Regular? Retrieval produces LTM that is independent of the hippocampus

• Neural mechanism for working memory and LTM would be different

AmnesiaAmnesia

• Reterograde– “Backward”

– Loss of info just prior to trauma.

• Anterograde– “Forward”

– Inability to add new information to memory.

Neurological examination of Amnesia Patients

• Based on Scoville and Milner's amnesic patient H.M., it has been known that the medial temporal lobes play a critical role in our ability to form new memories.

• Also demonstrated that not all forms of memory are equally affected by damage to the medial temporal lobes.

– Declarative or explicit memory is disrupted.

– Nondeclarative or implicit memory is largely intact, allowing patients to acquire perceptual and motor skills, conditioned responses, and to demonstrate priming.

Brain Tissue Removed from Henry Molaison (Patient H.M.)

Henry’s Performance on a Mirror-Tracing Task

HM mirror-tracing

HM could show implicit learning

Two Main Kinds of Memory: Declarative and Nondeclarative

There Are Several Kinds of Memory and LearningDamage to other areas can also cause memory loss.Patient N.A. has amnesia due to accidental damage to the left dorsal

thalamus, bilateral damage to the mammillary bodies (limbic structures in the hypothalamus), and probable damage to the mammillothalamic tract. Like Henry Molaison, he has short-term memory but cannot form declarative long-term memories.

Patient K.C. cannot retrieve personal (episodic) memory due to accidental damage to the cortex and severe shrinkage of the hippocampus and parahippocampal cortex; his semantic memory is good.

Two subtypes of declarative memory:

• Semantic memory—generalized memory

• Episodic memory—detailed autobiographical memory

The Brain Damage in Patient N.A.

Subtypes of Declarative and Nondeclarative Memory

Tests of Specific Attributes of Memory

Different Brain Regions Process Different Aspects of Memory

• Early research indicated that animals form a cognitive map—a mental representation of spatial relationships.

• Latent learning is when acquisition has taken place but has not been demonstrated in performance tasks.

• The hippocampus is also important in spatial learning.• It contains place cells that become active when in, or moving toward, a

particular location.

• Place cells remap when a rodent is placed in a new environment.

• Grid cells and border cells are neurons that fire when animal is at an intersection and at the perimeter of an abstract grid map, respectively.

Different Brain Regions Process Different Aspects of Memory

• Imaging studies help to understand learning and nondeclarative memory for different skills:• Sensorimotor skills, such as mirror-tracing.

• Perceptual skills—learning to read mirror-reversed text.

• Cognitive skills—planning and problem solving.

• All three of these depend on functional basal ganglia; the motor cortex and cerebellum are also important for some skills.

• Imaging studies of repetition priming show reduced bilateral activity in the occipitotemporal cortex, related to perceptual priming.

• Perceptual priming reflects prior processing of the form of the stimulus.

• Conceptual priming (priming based on word meaning) is associated with reduced activation of the left frontal cortex.

The Delayed Non-Matching-to-Sample Task

Memory Performance after Medial Temporal Lobe Lesions

Brain Regions Involved in Different Kinds of Learning and Memory