Memory can be classified based on what two aspects?
content and time course
How can memory time course be classified?
Short-term memory: temporary storage of information passive sensory trace
Working memory: storage and manipulation active exploitation of long-term memory
What is Working memory?
Working memory is the temporary activation of updated long-term memory networks for organizing actions in the near term
it is associative; it provides meaning and purpose, it has historical and behavioral context
it has a ’future perspective’, it is a ’prospective executive function’
it has an ancillary role under the supra-ordinate function of temporal organization
it is sustained attention focused on an internal representation. It is essential for all aspects of executive control and enables cognitive functioning beyond simple input-output mappings
Short: Working memory is the storage and active manipulation of information for organizing behavior
What are two models for working memory?
What does this show?
Individual prefrontal neurons fire persistently for memorized items
changes of firing frequency associated with the performance of a delayed response test
What is a common task to study working memory?
oculomotor delayed response task (ODR)
Monkey’s task: move the eyes (saccade) to the spot where a light was previously flashed
Individual PFC neurons are tuned to locations in space, i.e. they are maximally active for specific preferred locations
What is the delayed match-to-sample (DMS) task?
Monkey’s task: indicate whether the second shape (test) matches the first (sample)
Individual PFC neurons encode working memory content that is independent of motor commands
neuron activity is high during sample and delay time (higher for preferred object than nonpreferred object)
How does a neuron generate persistent activity?
Persistent activity can be explained by intrinsic (A) and network (B) mechanisms
if you change the properties of the simulation you can even generate spiking without external signals
B (1): Brain loops (sending signals to and from different parts of the brain) keep activation up
B (2): Localized network (passing on to neighbor neurons)
What is transient activity?
Vorrübergehende/flüchtige aktvität
Working memory is associated with bursts of oscillatory neural activity. What does this mean?
When analyzing low frequencies you can detect patterns
you can encode what is stored in specific neurons (informative regions)
What are advantages of transient activity?
Metabolically less expensive
Can handle encoding of multiple items
Explains limits on WM capacity
Better at resisting distractors
But: lack of correlation between gamma bursting and behavioral performance!
What is silent activity?
What does phase-dependent coding of working memory content mean?
The receiving/meaning of a signal might be dependent on the oscillatory of the receiver area
some signals might be received better than others
What monoaminergic results in neuromodulation of the PFC?
Prefrontal dopamine modulates the strength of working memory signals
What components does working memory have? And where are they?
Working memory has executive components (prefrontal cortex) and perceptual components (posterior sensory cortex). The topography of working memory is therefore the topography of its contents
What are three activities at cellular level?
At the cellular and local microcircuit level, current hypotheses include persistent (sustained) activity, transient activity and silent activity (synaptic storage)
At the whole-brain level, multiple cortical and subcortical regions interact to enable …
At the whole-brain level, multiple cortical and subcortical regions interact to enable the encoding, storage and decoding of working memory content
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