6 working memory

content and time course

• Short-term memory: temporary storage of information passive sensory trace

• Working memory: storage and manipulation active exploitation of long-term 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

• Individual prefrontal neurons fire persistently for memorized items

• changes of firing frequency associated with the performance of a delayed response test

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

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)

• 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)

Vorrübergehende/flüchtige aktvität

When analyzing low frequencies you can detect patterns

• you can encode what is stored in specific neurons (informative regions)

• 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!

• The receiving/meaning of a signal might be dependent on the oscillatory of the receiver area

• some signals might be received better than others

Prefrontal dopamine modulates the strength of working memory signals

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

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 the encoding, storage and decoding of working memory content