Lecture 8 - The remembering brain P1 Flashcards
the MTL system
medial temporal lobe
- includes the hippocampus and three cortical structures of the entorhinal lobe
the cortical structures of the entorhinal lobe are also referred to as:
the parahippocampal gyrus
how is info organised in MTL
- hierarchical organisation
- info is initially collected through the perihinal and parrahippocampal cortices then to entorhinal cortex then to hippocampus
what can the hippocampus be further divided into
dendate gyrus or CA subfields
anterograde amnesia
difficulties acquiring new memories
retrograde amnesia
difficulty remembering old memories
The case of H.M.
- had severe epilepsy
- so had bilateral MTL (removed hippocampus and amygdala)
- seizures stopped
- BUT - had minor retrograde amnesia and severe anterograde amnesia.
- global amnesa : affected all sensory modalities
- problems limited to declarative/explicit memory
HM and the digit span +1 test
normal subjects can do up to 18 digits
- after 25x trials, HM couldnt do more than 7 digits
(problem with transfer of info STM to LTM)
HMs implicit memory - mirror drawing task
HM substantially improved after 3x days of practice
- implicit memory intact
Wagner et al 1998 - remembered versus forgotten stimuli (aims)
- does the brain activity at encoding predict what items are later going to be recognised and which will be forgotten?
Wagner et al 1998 - remembered versus forgotten stimuli - findings
activity in the left ventrolateral PFC and the left MTL were predictive of later remembered versus forgotten stimuli.
Wagner et al 1998 - remembered versus forgotten stimuli - procedure
scanned Ps when they were studying a list of words that were subsequently tested in a recognition memory test.
after test - looked at brain activity during encoding to see if brain activity predicted which items are later going to be recognised/forgotten?
encoding specificity hypothesis
events are easier to remember when the context at retrieval is similar to the context of encoding
familiarity:
context-free memory in which recognised item feels familiar
recollection
context-dependent memory that involves remembering specific information from the study episode
familiarity/recollection corresponding brain region? (Eichenbaum et al 2007)
- the perihinal cortex processes item representations (important for FAMILIARITY)
- The parrahippocampal cortex is assumed to process ‘context’ (including scene perception)
- the hippocampus binds items in context (important for recollection)
Ranganath et al 2004
fMRI study that shows hippocampal activity in recollection
- whereas familiarity selectively activated perihinal cortex
activity with the perihinal cortex was predictive of the degree of familiarity based recognition
role of hippocampus
- encoding and retrieving constituent elements of an experience
e. g.
- names with faces
- locations of objects within a scene
what is consolidation
process that stabilises a memory over time after it is acquired
two types of consolidation
synaptic consolidation
system consolidation
what is synaptic consolidation
- structural changes int he synaptic connections between neurones
- may take hours - days to complete.
what is system consolidation
gradual shift of memory from hippocampus to the cortex related to declarative memory
(much slower)
Ribots law
- memory loss following brain damage has a temporal gradient
- more recent memories are likely to be lost
BECAUSE: remote memories have undergone systems consolidation - so don’t rely upon MTL anymore ARE cortex-dependent.
HM and Ribots Law
- HM demonstrated a degree of temporal gradient
- memories lost from 2 years prior
patient RZ and temporal gradient
- had Kosakoff’s syndrome
- unable to learn new paired associates
- remembered some famous people from 1930s but not after
two theories of system consolidation
standard consolidation theory : temp role of hippocampus
multiple trace theory : permanent role of hippocampus
standard consolidation model
initially, the hippocampus binds the information in many regions of the brain to form coherent episode
- overtime has less of a role
memory reacitvation (standard consolidation)
- reactivation is the core mechanism
- = reinstatement of patterns of neural activity in the cortex
- such reactivation subsequently results in STABILISATION and REFINEMENT of cortical traces
- this process leads to storage + recall relying solely on cortex (not hippocampus)
retrieval of nonconsolidated and consolidated memory
- any event contains different elements and sensory information
- hippocampus holds together different elements to get coherent episode
- hippocampus plays a role in reactviiating all elements in the early stages of memory existence - after consolidation this is no longer necessary
the temporal gradient in amnesia and semantic dementia
SD - damage to anterior temporal lobes (cortex)
AD: damage to hippocampus and related structures
SD patients can remember recent but not old events - as memories not dependent on cortex.
Multiple Trace Theory
- hippocampus has a permanent role in EPISODIC memory recall
- older memories have been reactivated many times
- each reactivation creates a new trace in MTL and in other neocortical structures
- the extent that damage is not global, older memories are more likely to be remembered as they have more traces
Gilboa at el 2004 - fMRI of remote personal memories (procedure)
- family members of Ps provided pictures of events
- from remote past to more recent time
- Ps scanned while thinking about the event and depicted its vividness
Gilboa at el 2004 - fMRI of remote personal memories - findings
- hippocampus activated for recent AND remote memories
- hippocampal activation was related to the richness of re-experiencing RATHER THAN the age of memory
place cells
neurons mapping locations within an environment. each neruon represents one location
grid cells
neurons in entorhinal cortex (EC) mapping multiple locations in 2-D environments
boundary/border cells
neurons in EC activate when the animal is near the borders of the environment
cognitive map theory
the theory that the hippocampus contains a spatial map of the environment
