This document is written in English and it contains a complete summary of chapters 8-15 for the second exam of Cognitive Neuroscience UU. Important terms are highlighted and concepts are clearly defined.
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Summary Principles of Cognitive Neuroscience for course UU Cognitive Neuroscience (200300074)
Samenvatting Principles of Cognitive Neuroscience hoofdstuk 8 t/m 15 (200300074)
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Cognitieve Neurowetenschap (200300074)
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COGNITIVE NEUROSCIENCE – EXAM 2 – CHAPTERS 8 – 15
,H8 | Memory: Forms and Mechanisms
8.1 Memory Stages, Processes, Systems and Tasks
Memoryis a series of processes by which the nervous system acquires information from new experiences, retains this
information for some time, and eventually uses it to guide behavior and plan future actions. There are 3 phases:
- Encoding; this consists of the processes by which experiences can change the nervous system. These changes
arememory tracescalled. This is thought to reflect changes in strength and/or number of synaptic connections between
neurons. Storage/storage: retainingmemory tracesduring the time. Long-term
- preservation requires cell- and system-level stabilization ("consolidation") processes.
- Retrieval: access to savedmemory traces, which can lead to a change in behavior. Sometimes
associated with the conscious experience of remembering.
To learnis used as a synonym ofencode. Can also describe gradual changes in behavior as a function. Learning here
refers to the combined effect of encoding, storage and retrieval – ultimately leading to an improvement in the
performance of a given task.
There are various memory systems. They can be defined as
groups of memory processes and associated brain regions
that work together to mediate performance of some peer
memory task.
- Random access memorymediates the retention
and manipulation of information for a few
seconds or minutes
- Long term memorymediates the retention of
information for extended periods
- Declarative memory(“explicit”) refers toconscious
memory for events (episodic) and facts (semantic)
- Non-declarative memory(“implicit") refers to memories expressed through achievements that are
independent of consciousness - Priming, Skills, and Conditioning.
8.2 Dissociation of Memory Systems
- Working Memory (WM) vs. Declarative Memory (DM)
Information on the distinction between WM and DM is provided by cases withamnesia, severe memory loss due
to:
- brain damage
O anterograde amnesia: amnesia developed after the injury retrograde
O amnesia: amnesia of things before the lesion
- normal lack of memory for events that took place during the first years of life(childhood amnesia) or
amnesia due to psychological trauma (psychogenic amnesia).
Memory loss due to brain lesions often results from bilateral damage to the medial temporal lobe. Unilateral damage here
leads to mild memory errors, as the spared medial region can take over some aspects. Bilateral damage results in severe
anterograde amnesia and some degree of retrograde amnesia. This prevents people from forming new memories. People
with amnesia can still hold a normal conversation, which implies that the WM is spared.
- the finding that people with amnesia (due to brain damage in medial temporal lobe) are impaired in
declarative memory, but not in WM = single dissociation
- a double dissociation requires patients with brain damage who have worsened WM, but not in DM. These
patients have also been identified, their lesions are often in the left temporoparietal cortex.
- Declarative (DM) vs. Non-declarative memory (NDM)
An important feature of medial temporal lobe amnesia is that it leads to errors in DM (as evidenced by recall and
recognition), but not in NDM (skill learning, priming).
Errors in NDM often arise after lesions in the occipital lobe.
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,8.2 Non-declarative memory
All forms of this have in common that they are expressed through achievement and are independent of
consciousness. There are 3 main forms of NDM:
- Prime: a change in the processing of a stimulus that is due to a previous, unconscious encounter with the
same or similar stimulus (-results from 1 single encounter)
- Skills learning: a gradual improvement in performance due to repeated practice (- requires
repeated learning trials)
- Conditioning: consists of simple responses to associations between stimuli (- also requires multiple
learning trials, but often between simple responses and associations).
8.3 Priming
Priming tests can'contaminated by explicit memory strategies'when a participant explicitly retrieves information from memory
(explicit recall) instead of applying the prime (unconsciously).
There are various forms of priming:
- Direct priming (prime and target stimuli are equal) O
Perceptual priming (test cue and target are perceptually related) Conceptual priming (test
O cue and target are semantically/associatively related)
- Indirect priming (prime and target stimuli are different)
OSemantic priming (prime and target are semantically related: 'envelope' and 'letter')
- Perceptual priming (Straight away)
Relies on brain structures that are different from declarative memory (especially episodic). Perceptual priming relies on
sensory regions of the cortex, such as visual regions of the occipital lobe.
Perceptual priming is impaired when:
- format of test stimuli changes between encoding and retrieval (study-test format shift)
- changes in modality (e.g. from auditory to visual presentation)
- introduction of more subtle changes (e.g. from uppercase to lowercase letters)
The greater the perceptual change, the greater the damping of perceptual priming.
Study-test format shifts affect perceptual priming, but not episodic memory. Conceptual manipulations have the opposite
effect: e.g. episodic memory is better at encoding tasks that favor semantic processing than for tasks that favor
perceptual processing. This effect is also calledlevels of processingcalled, and is the reason that you read what it says on
a test, instead of paying attention to the font. Episodic memory is thus sensitive to this, but perceptual priming is not
affected by it.
- this thus points to a double dissociation between perceptual priming and episodic memory. It supports the idea that these 2
forms of memory depend on different brain systems - perceptual priming on sensory cortices.
It is thought that the neural mechanism of perceptual priming leads to a reduction in neural responses. It has also been shown
that neurons in visual processing regions show a reduced firing level when a new visual stimulus is repeated. The termrepetition
suppressionis used to describe a similar and possibly related phenomenon observed in functional imaging techniques: Primed
stimuli result in weaker hemodynamic responses.
Various theories have emerged to explain why reduced neural activity (repetition suppression/neural priming) leads to
enhanced processing of a stimulus (behavioral priming). According to 1 theory, thesharpening theory: when a stimulus
is repeated, certain neurons start firing strongly that carry the important information with them. Neurons that are not
essential for processing the stimulus fire less and less, leading to diminished hemodynamic responses.
- Conceptual priming (Straight away)
2
, Conceptual priming reflects previous processing of conceptual aspects. It is sensitive to conceptual manipulations, but
not to perceptual manipulations. Conceptual priming does not depend on consciousness, and is preserved in amnesic
patients with mid-temporal lobe damage. Memory performance is impaired in these people in both perceptual and
conceptual memory tasks when the tests are explicit, but performance is normal when the tests are implicit. This
indicates that both perceptual and conceptual priming operate independently of the medial temporal lobe.
Alzheimer's patients are impaired in conceptual priming. This error suggests that conceptual priming is mediated by
brain regions affected in Alzheimer's but not amnesia, such as the lateral temporal and prefrontal cortices. This has also
been shown: conceptual priming is linked to the anterior part of the left inferior frontal gyrus; an area closely involved in
semantic processing.
- semantic prime (Indirectly)
In semantic priming, the prime and target have different names but are semantically related to each other. Participants
must make simple decisions about words in a certain sequence. Reaction times are faster for words preceded by
semantically unrelated words.
A theoretical framework for semantic priming is based on the assumption that semantic memory is organized in a
network, where each node corresponds to a concept, and each link corresponds to an association between two
concepts. When a node is reached (activated), and activation spreads through the network, the concepts are encoded.
This concept becomesspread activationcalled.
Thus, neural mechanisms of semantic priming would involve brain regions associated with the storage of semantic
knowledge, such as the left anterior temporal cortices. This is also seen in fMRI.
The purpose of semantic priming is likely to facilitate cognitive tasks in everyday life, such as reading
comprehension and problem solving.
- Rehearsal Enhancement
Priming is often associated with a decrease in activity (repetition suppression), but can also be associated with the opposite
effect: an increase in activity (repetition enhancement). Whether priming is associated with suppression or enhancement
depends on whether the stimuli has existing memory representations:
- stimuli that have existing representations; for this would priming onemodification of stored representations can
reflect. This leads to suppression and leads to access to a sharper representation
- stimuli that have no existing representation; this requires priming thecreation of new representations. This leads
to enhancement and possibly the retrieval of a new memory representation.
8.4 Skills Learning
Like priming, skill learning is independent of the medial temporal lobes and is preserved in patients with amnesia.
Skill learning appears to depend more on the interaction between the neocortex and subcortical structures such as
the basal ganglia. In everyday life, motor, perceptual and cognitive operations are closely linked in learning.
- Motor skill learning
Simple motor learning tasks can be divided into:
- motor sequence learning tasks: These focus more on the incremental acquisition of movements
towards well-executed behaviors
- engine adaptation tasks: these focus more on the process of compensating for environmental
changes.
-Motor sequence learning tasks: the best known is the “serial reaction time (SRT) task”. The best known example is
that 4 locations are presented on a screen with 4 corresponding keyboard keys. In each trial, a stimulus is
presented in 1 of the locations, and the participant presses the corresponding key. They are ignorant that the
sequence of stimulus location follows a repeated sequence, often one that is 10-12 units long. The result of such
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