Dynamic fading memory and expectancy effects in the monkey primary visual cortex

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Visual Processing

Background:

• Working memory (WM) is crucial for cognitive tasks.
• The role of the primary visual cortex (V1) in WM maintenance is debated.
• Understanding V1's contribution to WM can elucidate neural mechanisms of memory.

Purpose of the Study:

• To investigate the involvement of the primary visual cortex (V1) in working memory (WM).
• To determine if V1 plays an active role in maintaining WM contents during a delay period.
• To examine how V1 population activity relates to stimulus expectations and predictive coding.

Main Methods:

• Parallel, multisite recordings of multi-unit activity in monkey V1.
• Monkeys performed a delayed match-to-sample (DMS) task.
• Analysis of V1 population firing rate vectors during delay and test periods.

Main Results:

• V1 population activity maintained a fading trace of the sample stimulus during the delay period.
• This trace could be reactivated by impulse stimuli, enhancing neuronal firing.
• V1 responses to test stimuli were modulated by probabilistic stimulus contingencies, with reduced responses to expected stimuli.

Conclusions:

• The fading trace in V1 suggests intrinsic network dynamics rather than active, attention-dependent WM maintenance.
• V1's involvement in WM maintenance is likely passive, reflecting stimulus history.
• V1 responses align with predictive coding principles, showing reduced responses to expected stimuli.