Working Memory

• Working memory


  A cognitive system with a limited capacity that is responsible for temporarily holding information available for processing
• Maintenance (storage and rehearsal)

  Representations are symbolic codes for information stored either transiently or permanently in neuronal networks
• Control (elaboration)


  Operations are processes or computations performed on representations
• Working Memory


  Working (control) with your short-term memory (representations)
• The information-processing capacity of young adults is around seven elements, which George Miller called "chunks", regardless whether the elements are digits, letters, words, or other units

  • 7 +/- 2 "chunks"
• Different forms of working memory

  • Verbal working memory - verbal rehearsal
  • Visuospatial working memory - maintenance of spatial location, shapes, colors in short term memory
• Delayed - response tasks depend upon the animal's ability to maintain an internal representation over the course of a delay
• Only prefrontal lesions showed a selective and delayed-response tasks
• Jacobson (1936) concluded that the monkey's ability to use "immediate memory" was impaired
• Damage to the prefrontal cortex leads to working memory impairments
• Persistent neural activation during delays in the prefrontal cortex of monkeys
• The neurons encode that the food reward is in the right while the lid is closed ("a bridge in time"
• There is no homologue of the principal sulcus in humans
• We do not have clear anatomical landmarks as in the macaque case
• Persistent Activity in Human PFC
• Impact of PFC lesions on working memory
• TMS of Human PFC
• Excitatory connections within a population

  Mechanism to get neurons to keep firing
• Inhibitory connections


  Mechanism to get neurons to keep firing
• Attractor Neural Network


  Mechanism to get neurons to keep firing
• Continuous Attractor Neural Network

  Mechanism to get neurons to keep firing
• Bistability


  Network dynamics, established through positive/negative feedback loops of synaptic connections, give rise to bistability in stimulus selective networks
• Some single neurons can exhibit bistability due to intrinsic membrane properties
• Slow excitatory NMDA and inhibitory GABA currents maintain up and down states
• Fast AMPA excitatory currents switch states
• Neuromodulators (eg, dopamine) may deepen and increase the width of basins
• Increasing and Decreasing Delay Period Activity
• Oculomotor Delayed Response Task (ODR)