Spatial attention decorrelates intrinsic activity fluctuations in macaque area V4

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Visual Cortex Research

Background:

• Attention enhances processing of relevant stimuli and suppresses distractors.
• Internal neural activity, like ongoing firing fluctuations, can also act as noise.
• Previous research focused on external distractors, not internal cortical noise.

Purpose of the Study:

• To investigate if internal, ongoing cortical activity acts as task-irrelevant noise.
• To determine how attention modulates these internal neural fluctuations.
• To compare the impact of internal noise reduction versus signal amplification on neural processing.

Main Methods:

• Recorded neural activity from area V4 in macaques during an attention task.
• Analyzed neuronal firing variability and correlated low-frequency (<5 Hz) fluctuations.
• Measured the effects of attention on both firing rate and ongoing correlated activity.

Main Results:

• Neuronal firing to identical stimuli showed high variability.
• This variability was largely explained by correlated, low-frequency fluctuations in population firing rates.
• Attention directed to a stimulus reduced these correlated fluctuations.
• Attention-dependent reduction in internal noise improved signal-to-noise ratio more than increased firing rates.

Conclusions:

• Ongoing correlated cortical activity functions as internal noise.
• Attention actively suppresses this internal noise.
• Reducing internal noise is a key mechanism by which attention enhances signal quality in the visual cortex.