Working Memory – Neurology

As working memory (WM) is not a singular process, there is no singular brain structure responsible for it. What we call working memory is the “result of the interaction among several brain regions,” and any “particular item maintained in working memory will be coded in a highly distributed manner.”​^​1​​ Which parts of the brain are involved in any given task:

“….depend on a number of factors, including the type of material to be remembered, the task (e.g., simple maintenance or additional manipulation requirements), and also which stage of the dynamic interplay of processing components that is considered (e.g., during encoding, the delay period, or the response phase).”^​1​

Brain Regions

• Basal Ganglia (BG)^​1​
  • Correlated with WM capacity
  • BG activity is negatively correlated with “the unnecessary storage of distracting information.”
  • Striatum^​1​
    • Part of the BG
    • Controls “when PFC representations should be maintained versus updated.”
    • Reduced levels of dopamine in the striatum impairs its ability to update the PFC representations.
• ​Cerebellum^​1​
  • “Commonly activated in working memory tasks.”
  • Thought to “support verbal rehearsal, but may contribute to working memory more generally.”
• Parietal Cortex^​1​
  • Bilaterally activated during spatial WM tasks, though with “some lateralization toward the right hemisphere”​
  • The left inferior hemisphere has been associated with verbal WM.
  • The Superior parietal cortex is thought to be the location of selective attentional control.
  • Activity in the parietal cortex increases with the number of items being remembered by WM, leveling out at 3-4 items.​
• Prefrontal Cortex (PFC)^​1​
  • Highly involved in WM, and likely contributes to it in several ways.
  • The left ventral PFC appears to be more involved in verbal working memory.
  • The lateral PFC seems particularly involved with “resilient information maintenance.”
  • Higher activation in the left PFC “at baseline has been linked to more effective down-regulation of emotional responses to aversive events […] and to greater psychological well-being.”^​2​
  • “[A]ttempting to appraise emotional stimuli in nonemotional terms increases activation” in both the lateral & medial PFC.^​2​
  • Dorsolateral PFC (dlPFC)^​1​ 
    • Involved more in the “updating and ordering of working memory content (i.e., manipulation tasks)” than in maintenance tasks.
    • The right dlPFC appears to be more involved in spatial WM than verbal.
• Temporal Cortex^​1​
  • Has been associated with visual WM.
  • Superior temporal activation is considered for verbal WM.
• Sensory Regions^​1​
  • The same regions “dedicated to sensory processing are believed to store sensory information” as a part of WM activity.
  • During WM, “different stimulus categories, such as faces and houses, activate category-specific regions of the ventral visual cortex.”
  • Fascinatingly, research has “demonstrated that the particular content held in visual working memory can be decoded from activity patterns in visual cortex.”

Neurotransmitters

Dopamine

Dopamine is an important factor in WM. As noted above, reduced levels in the striatum impairs the updating of PFC representations.^​1​ As people with low WM have trouble ignoring distracting information, “the gate-keeping function of fronto-striatal regions and associated dopamine mechanisms is thus one likely source of the capacity limits of working memory.”​^​1​

At least one study looking at the brain’s dopamine D1 and D2 systems before and after participating in a WM training program, and they reported changes in cortical D1 receptors and striatal D2 binding.^​1​

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