In a delayed-response task, a monkey watches food hidden under one of two cups, waits 15 seconds, and then reaches. During the delay, a brief loud noise is introduced. The monkey reaches for the wrong cup. The neuroscientific explanation is:
AThe memory trace decayed passively from a short-term storage buffer during the long delay
BThe hippocampus failed to consolidate the spatial memory into long-term storage before the delay ended
CThe distraction interrupted the sustained PFC neuronal firing that was actively maintaining the spatial information online
DThe loud noise activated competing motor programs in premotor cortex that overrode the stored location
Working memory in the PFC exists as sustained firing — neurons continue firing throughout the delay period to keep spatial information 'online.' This firing is vulnerable to disruption: a distractor can knock the population out of its maintained state, and the information collapses immediately. This is not passive decay (option A) but active disruption of an active process. The hippocampus (option B) is involved in consolidating long-term memories, not maintaining brief working memories during delays.
Question 2 Multiple Choice
A patient with PFC damage cannot hold a phone number in mind long enough to dial it, but their long-term memory for facts and events is intact. Which conclusion best fits this pattern?
AWorking memory and long-term memory are the same system; PFC damage only affects recently encoded memories within hours of learning
BWorking memory depends on active sustained PFC firing to maintain information online, while long-term memory involves different structures and mechanisms that are unaffected
CThe PFC stores phone numbers in synaptic weight changes; the intact long-term memory shows that the PFC is not truly damaged
DLong-term memory is localized entirely in the PFC; the preserved long-term memory in this patient shows the case is atypical
This double dissociation — impaired working memory, intact long-term memory — supports the conclusion that they are distinct systems with different neural substrates. PFC damage disrupts the active maintenance mechanism (sustained firing) that keeps information online for immediate use, while hippocampal-cortical systems supporting long-term memory consolidation are unaffected. Long-term memories don't 'live' in PFC as active firing; they are stored in synaptic changes elsewhere.
Question 3 True / False
The prefrontal cortex stores working memory information in lasting synaptic weight changes, similar to how long-term memories are consolidated in hippocampal circuits.
TTrue
FFalse
Answer: False
Working memory in PFC is maintained by sustained action potential firing — neurons remain active throughout the delay period to represent information that is no longer perceptually present. This is fundamentally different from long-term memory consolidation, which requires synaptic potentiation and structural changes over hours to days. When PFC firing is disrupted (by distraction, cooling, or direct interference), working memory vanishes instantly — exactly what you'd expect for a system based on ongoing activity rather than permanent structural storage.
Question 4 True / False
Working memory capacity is limited partly because each additional item loaded requires a separate neural population to sustain firing, and competing populations interfere with each other's signal fidelity.
TTrue
FFalse
Answer: True
The biophysical basis of the ~4-7 item capacity limit lies in the competition between simultaneously maintained representations. Each sustained firing population must maintain its signal against background neural noise and against interference from other active populations. As more items are loaded, the signal-to-noise ratio for each representation degrades. This explains both the capacity ceiling and why adding a single item beyond capacity can cause multiple items to fail simultaneously.
Question 5 Short Answer
Why is it more accurate to say the prefrontal cortex 'actively maintains' working memory rather than 'stores' it, and what does this distinction predict about the effects of distraction?
Think about your answer, then reveal below.
Model answer: Working memory exists as ongoing neural activity — sustained firing of PFC pyramidal neurons that must be continuously maintained against noise and competing signals. Unlike storage, which is passive and persistent, active maintenance is fragile: anything that interrupts the firing pattern (a distractor, cooling the cortex, magnetic stimulation) immediately destroys the representation. This predicts that distraction during a delay will cause immediate forgetting, not gradual decay — which is exactly what experiments show.
The storage metaphor implies a box where information sits until retrieved. The active maintenance view implies a process that must be continuously run. These have different predictions: a storage system would survive brief interruptions; an active maintenance system would not. The fragility of working memory to distraction — and the specificity of that disruption to ongoing delay activity — is strong evidence for the active-maintenance account.