Classify memory and describe the mechanism of its formation. Describe the areas concerned with speech and the types of aphasia.

Definitions

Types of Memory

Long-term memory is of two kinds

Consolidation and the Hippocampus

New information → Short-term memory (reverberating circuits) → Consolidation — requires the hippocampus and protein synthesis → Long-term memory stored in the cortex

• Bilateral hippocampal damage causes anterograde amnesia — the patient cannot form new declarative memories, though old memories and skill learning are preserved. The classical case is patient H.M.
• Papez circuit — hippocampus → fornix → mammillary body → anterior thalamus → cingulate gyrus → back to hippocampus
• Korsakoff psychosis — thiamine deficiency damages the mammillary bodies → amnesia with confabulation

Cellular Basis — Long-term Potentiation

High-frequency stimulation of the hippocampal pathway → Glutamate released → AMPA receptor depolarises the membrane → Mg2+ block removed from the NMDA receptor → Ca2+ influx → Kinase activation, more AMPA receptors inserted → Strengthened synapse — LTP

• LTP is the accepted cellular model of memory
• It shows the two properties memory needs — it is associative and long lasting
• Late LTP requires new protein synthesis, which is why protein synthesis inhibitors block long-term but not short-term memory

Speech and Cerebral Dominance

• 95% of right-handed and about 70% of left-handed people have left hemisphere dominance for language
• The dominant hemisphere handles language, calculation and analysis; the non-dominant handles spatial relations, music and face recognition

Types of Aphasia

• The Broca aphasic knows what he wants to say but cannot say it, and is therefore frustrated; the Wernicke aphasic talks fluent nonsense and is unaware of it

Types of Learning

• Habituation and sensitisation are non-associative; conditioning is associative

Applied Aspects

• Alzheimer disease — loss of cholinergic neurones in the nucleus basalis of Meynert and hippocampal degeneration; amyloid plaques and neurofibrillary tangles. Treated with anticholinesterases
• Electroconvulsive therapy and head injury cause retrograde amnesia by disrupting consolidation
• Alcohol impairs consolidation → blackouts, with no memory of events despite being conscious at the time
• Aphasia versus dysarthria — in dysarthria language is intact but articulation is faulty
• Sleep is essential for memory consolidation — slow-wave sleep for declarative and REM sleep for procedural memory
• Testing memory clinically — immediate (digit span), recent (3 objects at 5 minutes) and remote (personal history) are affected differently by disease
• Transient global amnesia — sudden isolated anterograde amnesia lasting hours, with full recovery
• Bilingual aphasia — languages may recover at different rates after a dominant hemisphere stroke