Memory

Human Neurobology 217Jana Vukovic

jvukovic@anhb.uwa.edu.au

Key points:

• Famous cases of memory deficit

• Brain structures involved – hippocampus

• Circuitry of memory – Papez Circuit

• synapse strengthening and long-term potentiation (LTP)

What is memory?

• Memory is defined as the acquisition, storage, and retrieval of information.

• All animals learn things from their interaction with the environment

• Human brain forms memories more effectively than others

• Maximum behavioural flexibility and most efficiently adaptation to environment.

time

Brain damage occurs

Anterograde amnesiaCannot later remember

events that occur after brain damage

Retrograde amnesiaCannot remember

events prior to brain damage

Amnesias = memory disorder

HM & NA• Which brain structures were removed from HM’s brain?

– Hippocampus, hippocampal gyrus, amygdala, uncus were removed on both sides

• Which brain structures are damaged in NA?– Thalamus and medial temporal lobe, mammilary bodies missing on

both sides

• Can HM and NA form new long-term memories (declarative)?– NO.

• Can HM and NA learn new skills (procedural)?– YES.

• What kind of amnesia do HM and NA have?– Sever anterograde amnesia.

NA

• Korsakoff's syndrome: – Found mostly in alcoholics who get most of their calories

from alcohol and become vitamin deficient (thiamine deficiency)

– Damages mammilary bodies and other nearby parts of the hypothalamus and thalamus

– This damage produces an amnesia similar to the type of NA and HM (sever anterograde amnesia)

• Altzheimer’s disease: – Loss of neurons in hippocampal and prefrontal cortex

produce first signs of memory loss.

• Long-term memories are biologically different from short-term memories

• Long-term memories are stored throughout the brain, but the hippocampus is necessary for the information to reach long-term storage.

Declarative Memory (explicit)

Procedural Memory (implicit)

Long-term memory

Remembering events

(episodic m.)

Knowing facts(semantic m.)

HippocampusNearby cortical areas,

diencephalon

Skills and habits

Emotionalassociation

Conditionedreflexes

StriatumMotor areas

of cortexcerebellum

amygdala cerebellum

Hippocampus

• Essential for declarative memory

• Cylindrical structure

• Longitudinal axis surround thalamus

Out put from hippocampus

Prefrontal cortex

Association cortex

Cingulate gyrus

AnteriorThalamic nuclei

Mamillary body

HypothalamusAmygdala

Hippocampal formation

fornix

Mammillothalamic tract

Strengthening of synapses

• Long-term potentiation (LTP) is the long-lasting strengthening of the connection between two neurons

• can last from hours to days, months, and years.

Long-term potentiation of synapses• Hippocampal slice preparation to study LTP

• single stimulation to input path

• measure hippocampal response baseline

• Give train of stimulation to input path

• Again give single stimulation to input path

• hippocampus response is larger (potentiated)

• Give single stimulation a week later

• Hippocampus response still potentiated (long term potentiation)

Synapses are strengthened

More dendritic spines on dendrites where new synapses are made

Dendritic spines from a cerebellar Purkinje cell, drawn by Cajal (Ramón y Cajal, 1899b).

Long-term potentiation

Only strong stimulus will dislodge Mg2+ from the NMDA receptor

Exercise and trophic factor production in the adult brain

Describe Papez circuit?

Last Slide