Memory
Definition: recording
retention
and retrieval of knowledge
Various forms of learning – various memory systems
MEMORY
Short term
Long term
DECLARATIVE (Explicit) NONDECLARATIVE (Implicit)
FACTS EVENTS SKILLS PRIMING CLASSICAL NON-ASSOCIATIVE LEARNING
CONDITIONING
EMOTIONAL MOTOR
RESPONSE
Skills: perceptual, motor, cognitive. Also called procedural memory
Memory: temporal properties
(Sensory or Echo M: milliseconds, sensory stimuli in the respective cortical areas)
Immediate M: eg. recall without delay (7 digits)
Short-term M (working M): storage, presentation, action, retention
Long-term M: permanent and large stores – semantically organized
Cognition and memory
Cognition: mental processes of knowing.
Includes:
high-level perception
attention
memory
frontal lobe functions
praxis
language (speech, writing, reading)
reasoning
etc etc
Fluid and crystallized forms
Papez circuit and the limbic system
Papez (1937) : a circuit important in memory and emotion
hippocampal cortex
fornix
mamillary bodies
mamillo-thalamic bundle (Vic D’Azyr)
thalamus (anterior and dorsomedial nuclei)
cingulate cortex
Connections:
inputs: entorhinal cortex isocortical associative areas (via the hypothalamus)
amygdala
outputs: diffuse cortical areas (via the cingulate cx)
Importance of the circuit:
provides continuous reintegration of information
a lesion anywhere along it may interfere with memory
Fronto-subcortical circuits
Somatotopically organized
Parallel frontal cortex
Distinct
Role in:
motor activity
emotions
ocular motion thalamus striatum
behavior
memory
pallidum
pallidum
Anterior cingular circuit:
anterior part of the cingulate gyrus (Br 24)
“limbic” striatum: n. accumbens, olfactory tubercule, VM caudate
globus pallidus
thalamus (paramedian part of DM nucleus)
anterior part of the cingulate gyrus
The anatomy of the different memory systems
A. Declarative memory
Dichotomy between:
Domain-specific and domain-independent regions
Neocortical regions Medial structures
same object, different aspects medial temporal region
(eg. hammer) diencephalic structures
basal forebrain
Damage to neocortical regions domain-specific retrograde and anterograde amnesia
Damage to the medial structures widespread deficits of declarative memory
bilateral global amnesia affecting all domains of declarative memory
unilateral left: verbal memory loss
right: non-verbal memory loss
B. Nondeclarative memory
Various subtypes, dependant on the same regions that mediate performance in a given domain.
Motor skills: pyramidal, extrapyramidal and cerebellar systems
Perceptual repetition priming: modality-specific neocortices (visual priming: visual cx)
Conceptual repetition priming: polymodal linguistic neocortical regions
Classical conditioning: cerebellar (dentate and interpositus nuclei)
C. Working memory (short-term memory)
Dorsolateral frontal areas
direct the immediate memory stores
right: spatial information (right parietal lobe)
left: verbal information (left temporal or parietal)
D. Immediate memory
Posterior neocortical regions
modality-, and material-specific
auditory visual verbal nonverbal
Memory systems: a summary of anatomical correlations
MEMORY
Short term
Long term
DECLARATIVE (Explicit) NONDECLARATIVE (Implicit)
FACTS EVENTS SKILLS PRIMING CLASSICAL NON-ASSOCIATIVE LEARNING
CONDITIONING
EMOTIONAL MOTOR
RESPONSE
TEMPORAL LOBE STRIATUM CORTEX AMYGDALA CEREBELLUM REFLEX PATHWAYS
DIENCEPHALON
Working memory (Baddeley; Goldman-Rakic et al.)
multimodal
input: sensory reality
previous memories
ideas, projects other cortical areas
makes incoming information available (representative memory) and manipulates it „on-line“
↓
decision making
↓
movement or behavioral change
As the system has manifold inputs, missing inputs may lead to „frontal lobe signs“ without an actual frontal lobe lesion (see cortico-
subcortical circuits).
Working memory is subserved by two systems in the frontal lobe:
Dorsolateral cortex (9, 46) - spatial working memory (Delayed Reaction, Delayed Alternation)
Ventrolateral cortex (45, 47/12) - non-spatial (verbal) working memory
These systems are extensively connected to other cortical regions
Hypothesized functioning:
Step 1.: VL cortex, organization of information retrieved from short-term memory
Step 2.: DL cortex, active manipulation and further processing of the information
In healthy volunteers PET examinations during psychological testing verified this hypothesis:
1. „block tapping teszt“ – 9 squares – place and consecutive order – VL cortex
„box opening “ – requires manipulation of information and strategy – DL cortex
Alzheimer’s: a model of the importance of different structures in memory processes
Course of the disease (modified after Braak and Braak)
Entorhinal stage – transentorhinal and entorhinal cx - symptom-free
Limbic stage – hippocampus and subiculum - mild dementia
Isocortical stage – associative and primary sensory cx - severe dementia
Gradual isolation of the hippocampus from the connected cortical and limbic structures
Schematic representation of short-, and long-term memory
Environmental Sensory registration Short-term Long-term
stimuli retention retention
visual (working M)
auditory practising
tactile encoding
decision
recall strategies
Outgoing
reply
The limbic system: clinical importance
Appendix 1.
Klüver-Bucy syndrome
hypersexuality
hypermetamorphosis (constant exploration of environment, mostly with the hands)
bulimia
oral tendency
aphasia, amnesia, dementia
Causes: bilat. temporal lobectomy, herpes simplex encephalitis, Pick, Alzheimer
Appendix 2.
Learning and memory: some basics
Basic elements of learning:
habituation and sensitization (ie. decreasing and increasing presynaptic transmitter release).
Long-term memories require mRNA and protein synthesis (sign of structural changes)
Long-term potentiation: mechanism of associative learning?
Role of the hippocampus:
imprinting of memories
connection (association) of various kinds of sensory information
is not directly involved in long-term retention
Electrophysiologically, two phases: theta activity – memory acquisition (eg. exploration of environm.)
sharp waves – memory consolidation (rest, feeding, …)