The MTL role in memory and perception

Contents The Medial Temporal Lobe - Anatomy

The Medial Temporal Lobe and MemoryHippocampus, Basics and the traditional view

Functional specialization within the MTL

Beyond declarative memory

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The MTL and LTM – the traditional view

Dissociation between declarative and procedural memory in amnesia.

Dissociation between short and long term memory in amnesia

Consolidation and the hippocampus – HM

A single system in the MTL crucial for declarative memory – a unitary view

The hippocampus plays only a temporal role in memory formation

Ofrit

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The MTL in recognition memory

Recollection and familiarity Evidence from normal performance

ERP evidence for different timing

Evidence for anatomical dissociation from amnesia.

Evidence from fMRI

Functional distinctions within the MTL

Two independent MTL networks: The hippocampal-diencephalic (hippocampus, fornix, mamillary bodies and anterior thalamus) – critical for encoding an recall for episodic information.

The non hippocampal MTL (perirhinal cortex and medial dorsal thalamus) – critical for familiarity judgments.

Natalie

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Different manipulation-effects on recollection and the sense of familiarity

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ERP dissociations

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MTL and amnesia

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Transient cerebral hypoxia (which impairs primarily the hippocampus) reduces performance in relational tests but not so much item recognition.

ButThe anatomical resolution of such lesions is poor

YetSimilar findings were reported from lesions studies in animals (rats)

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Brain activations during recollection of items and sense

of familiarity Recollection-related activity is reflected by the contrast between “remember” and “know”

Familiarity-related activity is reflected by contrasts between “know” and “misses”

משימה Hippocampus PPHG APHG

Recollection of items 84% 58% 11%Recollection of associations 100% 50% 67%Familiarity 27% 27% 87%

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Further fractionalization of the MTLA related view: The hippocampus is involved in rapid learning of associations between individual items and their context, while the parahippocampal region, particularly the perirhinal cortex support memory for individual objects.

The “Binding of item and context” (BIC) model:

Three functionally distinct MTL regions:

Perirhinal cortex (responsible for encoding and retrieving of information about items.

Posterior parahippocampal cortex stores information about context.

The hippocampus binds the item with the context.

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The role of the MTL in memory: The alternative view

The hippocampus and the perirhinal cortex are differently involved in memory:

Hippocampus and the parahippocampus - recollection

Perirhinal – familiarity

All MTL structures (including the hippocampus) are continuously involved in encoding and retrieval.

The Multiple-Trace Theory (MTT)

Reut

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Beyond declarative memory

MTL (focus on hippocampus) amnesia a patient’s view.

The role of MTL in visual discrimination

The role of the MTL in oddity judgments

Outstanding questions and future directions

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Visual discrimination and MTL

The perirhinal cortex is the apex of the ventral system.

It is responsible for processing and storing of representations of complex feature conjunctions

Resolving “feature ambiguity”

A view of the Rhinal cortex

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MTL functional seggregation

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Relating the input to MTL to its roles

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A patient’s view

“The areas of my life that I find most challenging are when I am given a series of directions, remembering my way around somewhere (familiar or unfamiliar1), how I got into a building and how I can get out of it again, driving somewhere not only for the first time, but many times, remembering where I left my car and how I got into the car park in the first place, which way to turn out of a car park to get home . . .. Whichever angle I look, everything looks the same”.

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Feature ambiguity study - stimuli

Monkeys (Bussey & Saksida, 2002) Humans (Barens et al., 2005)

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Feature ambiguity studys - results

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