Chapter 11 Flashcards
What is memory?
- Plasticity is the brain’s ability to change as a result of experience; persists throughout life (although greatest in childhood).
- Learning and memory is a brain-level property rather than a specialized faculty.
- Different regions of the brain contribute to learning and memory in different ways – some regions are specialized for words, others for perceptual learning, and others for remembering episodes from one’s life.
HM
- H.M. had epileptic seizures at age 10.
- Surgical resection of bilateral medial temporal lobes including hippocampus at age 27 resulted in profound amnesia.
- One of the most cited articles in cognitive neurosciences.
Taxonomy of short-term memory - phonological short term memory
Capacity limit of phonological STM assessed by span tasks:
- Miller (1956) suggests span is 7 +/- 2 meaningful “chunks”.
- Others argue that limit is lower, and chunking relies on LTM.
- Limit may be lower if information not rehearsed (e.g. articulatory suppression through mouthing irrelevant speech).
Capacity not strictly related to meaningfulness of chunks because:
- Span length lower for polysyllabic words (skeleton, binoculars etc.).
Span length lower for phonologically similar words (map, cat, cap etc.).
Taxonomy of short term memory - visuo-spatial short-term memory
- Luck and Vogel (1997): brief displays of arrays of oriented coloured lines; suggests capacity limitation of ~4 objects.
- Ranganath et al. (2004): maintaining single object in STM involves activating ventral stream representations.
- Likely source of activation from parietal areas (e.g. selected & sustained attention) and prefrontal cortex (task setting).
- IPS activity related to intra- and interindividual differences in capacity (Todd & Marois, 2004, 2005).
Taxonomy of short-term memory - working memory
Information is passively retained in limited capacity short-term stores (e.g. phonological STM, visuo-spatial STM)
- These short-term stores lie posteriorly (e.g. parietal lobes), with content of information also in sensory regions (see Ranganath study).
The PFC is responsible for refreshing information in the stores (rehearsal) and manipulating that information (e.g. using the list of numbers in STM to perform calculations)
- E.g. the “central executive” in Baddeley and Hitch (1974)
Taxonomy of short term memory - Petrides’ Theory of Working Memory
Division of PFC into at least two separate processes – maintenance (VLPFC) and manipulation (DLPFC).
What is amnesia?
- Most amnesics have difficulties in acquiring new memories (anterograde amnesia) and remembering events from before their brain injury (retrograde amnesia) although extent of each is variable.
- Amnesia can arise from neurosurgery (e.g. HM), strokes, head injury, certain viruses or as a symptom of Alzheimer’s dementia.
Functions of HC and MTL in memory - Ribot’s law
Consolidation = the process by which moment-to-moment changes in brain activity are translated into permanent structural changes.
What memory systems are less impaired in amnesia - short term memory
- Amnesics have normal digit span (Baddeley & Warrington, 1970).
- HM could remember a number for 15 minutes by continuously repeating, but forgot it within 1 minute of stopping and had no recollection of attempting it (Milner, 1971).
What memory systems are less impaired in amnesia - non-declarative memory
- They can learn new skills (procedural memory) – e.g. HM’s mirror drawing.
- Amnesic patients can learn the rules of a weather prediction game, but cannot remember which cards they have previously seen.
- Patients with Parkinson’s disease show the opposite pattern.
- Amnesic patients show priming in stem completion (DEFEND, DEF___) despite inability to recollect word.
- Amnesic patients improve on the Gollin Incomplete Figures Test despite inability to recollect having done the task before.
What memory systems are less impaired in amnesia - semantic memory
- Amnesic patients have generally intact semantic memory, but does this reflect the fact that most semantic knowledge is acquired early in life?
- Amnesic patients have generally better memory for early life (Ribot’s law).
- Other amnesics are able to learn some new semantic knowledge, but whether they learn at the same rate or use the same mechanisms is debatable (e.g., a lot of repetition helps; spared cortex involved?).
Consolidation theory
Type of information: episodic and semantic memories; duration of storage: temporary (years); relationship to cortically based memories: memories transferred from hippocampus to cortex; explanation of amnesia: old memories are not stored in hippocampus so spared by damage.
Multiple-trace theory
Type of information: contextualised memories; duration of storage: permanent; relationship to cortically based memories: memories in cortex are more schematic (lack content) and more semantic-like; explanation of amnesia: old memories have less rich context and so spared by damage.
Cognitive map theory
Type of information: spatial memories; duration of storage: permanent; relationship to cortically based memories: HC stores spatial info whereas cortex stores other kinds of info.
Memory and the prefrontal lobes - role of PFC in working (with) memory
- Prefrontal cortex (PFC) of frontal lobes is involved in online maintenance and manipulation of information.
- This includes working memory (i.e. manipulation of information currently held in short-term stores).
- Also includes “working with memory” (i.e. encoding, retrieval and evaluation of information stored in long-term memory).
- Patients with PFC lesions often have disorganized memory.
- Similar role in long-term memory as in working memory.
- Many researchers maintain distinction between ventrolateral (VLPFC) and dorsolateral (DLPFC) divisions.
- Also evidence in humans of different functional specialization of right and left hemispheres.
