Exam 4

• Working memory


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

  1. Representations are symbolic codes for information stored either transiently or permanently in neuronal networks

  2. Ex: Keeping a cellphone number in storage (maybe ba covertly repeating it) until you save it in your phone
• Control (elaboration)


  1. Operations are processes or computations performed on representations

  2. Ex: Articulatory control for the rehearsal (inner voice)
• Working Memory

  Working (control) with your short-term memory (representations)
• Limited Capacity


  • The information-processing capacity of young adults is around seven elements, which he 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
• Verbal working memory


  Verbal rehearsal, e.g. remembering a cell phone number
• Visuospatial working memory


  Maintenance of spatial location, shapes, colors in short term memory, e.g. anything that involves the manipulation of a visual representation, like remembering sequence of events, mentally navigating and even doing math
• Prefrontal Cortex and Working 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 impairment
  • Jacobson (1936) concluded that the monkey's ability to use "immediate memory" was impaired

  
• Experimental Lesions of Monkey Prefrontal Cortex

  Damage leads to working memory impairments
• Electrophysiology of Monkey Sulcus Principalis (i.e., main sulcus in the prefrontal cortex in monkeys)


  Persistent neural activation during delays

  
• Persistent activity


  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
• Modeling Persistent Activity


  • How can we get neurons to keep firing?
  • Excitatory connections within a population
  • Inhibitory connections
  • Attractor Neural Network

  
• Neural networks


  Continuous Attractor Neural Network

  
• 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)
• Cognitive control


  The ability to focus on information that is currently relevant to a particular goal, while inhibiting information that is not relevant
• Cognitive control

  • Dependent on multiple executive functions, including working memory, inhibition, conflict monitoring, and has often been discussed in terms of facilitating flexible behavioral responses
• Proposed functions of cognitive control

  • Attention (vs. orienting) – think 'top down'
  • Active maintenance (working memory)
  • Task switching
  • Strategic Retrieval
  • Inhibitory control
  • Performance monitoring
• Harlow, John Martyn (1868). "Recovery from the Passage of an Iron Bar through the Head". Publications of the Massachusetts Medical Society
• Inhibition Tasks


  • Flanker task
  • Antisaccade Task
• Human patients with damage to frontal lobes have difficulties suppressing the "reflective" saccades
• Neural Recordings During Antisaccade Task
• Neural Recordings During Countermanding Task
• fMRI of Inhibition of Manual Movements
• Performance Monitoring


  Theories of the regulation of cognition suggest a system with two necessary components: one to implement control and another to monitor performance and signal when adjustments in control are needed

  
• During task preparation, the left dorsolateral prefrontal cortex (Brodmann's area 9) was more active for color naming (hard) than for word reading (easy)


  Consistent with a role in the implementation of control
• The anterior cingulate cortex (Brodmann's area 24 and 32) was more active when responding to incongruent stimuli


  Consistent with a role in performance monitoring

  
• Modeling conflict and cognitive control