MEMORY SYSTEMS IN THE BRAIN Some Gross Anatomy

The Human Brain saggital section at midline

THE “FUNCTIONAL NEUROANATOMY” of MEMORY Medial temporal lobe structures –Hippocampus –Parahippocampus (entorhinal cortex) –Encoding and consolidation of declarative memory –Role in recent LTM retrieval –Damage leads to “classic” amnesia: severe anterograde declarative deficit –Some evidence for LH verbal, RH spatial

Lateral temporal lobe structures –retrieval of declarative memory? –Representation of semantic knowledge? –“convergence zones” that index the attributes of an episode? –LH semantic, RH autobio? Frontal lobe structures –Anterior areas most involved in memory function (prefrontal, basal forebrain) –Lateral regions linked to working memory –Medial regions linked to executive control and attention –Role in strategic aspects of memory –Damage leads to deficits in “effortful” aspects of remembering, confabulation

Diencephalon –Thalamus, Hypothalamus, Mammilary Bodies –Close links to frontal, prefrontal cortex –Role in activation of retrieval process –Damage can lead to amnesia that resembles hippocampal syndrome Basal Ganglia, Cerebellum –Storage, activation of procedural skill and memory –Damage leads to apraxia, deficits in the initiation and control of action Posterior “Association” cortices –More “abstracted” than sensory regions –Representation of sensory-motor aspects of memories?

fMRI studies of EPISODIC MEMORY Explosion in work Tulving’s HERA model (Hemispheric Encoding and Retrieval Asymmetry) Encoding of episodes –Effortful encoding / semantic activation Left PFC, temporal/fusiform, anterior cingulate –Orienting / novelty/context? Medial temporal, hippocampal complex; left for verbal, right for spatial (Dolan & Fletcher, 97) –Mixed evidence for retrieval-success correlations

Retrieval of episodes –Retrieval mode and effort Right PFC, maybe anterior cingulate and cerebellum, hits and CRs (Buckner, 98) Inhibition of lateral temporal region, bilaterally –Access and activation of traces Medial temporal lobes, hippocampal complex activity correlates with subsequent success/failure –Further localization has been controversial Regions of hippocampus, hippocampus versus parahipp, entorhinal, etc. dissociate in various ways (see Mayes)

A recent example: memory- contingent activity via fMRI –Casasanto, et al. (2002) –240 sentences (“they buried the money”) (RSVP?) or length-matched asterisks –Intentional memory task –Yes/no recognition of old & new sentences –MRI scanned during encoding –Sentences – controls (subtraction) Left IPFC (pos corr with d’) Left Middle temporal gyri Right superior temporal gyri (negative corr) Within MTL: –+corr for hippocampus, parahipp, and fusiform gyryus bilaterally

MEMORY-CONTINGENT fMRI Wagner, et al. (1998) –Event-related fMRI –Word 2 sec SOA –LIFC and L parahipp activity greater for subsequently remembered words Brewer, et al. (1998) –Event-related fMRI –Complex scenes –RFC, bilateral parahipp activity greater for subsequently remembered scenes

CURRENT CONTROVERSIES –How localized are memory functions? –Are processes content-specific? –What is the neurobiological relation between episodic, autobiographical and semantic memory? –What is the role of the various MTL structures in episodic attention, encoding, storage and retrieval? –What changes over time? –What is the role of moderating variables like social context, IQ, age, time since damage, etc. on the neurobiology of memory?