  Previous studies have demonstrated the importance of the primary sensory
cortex for the detection, discrimination and awareness of visual stimuli, but
it is unknown how neuronal populations in this area process detected and
undetected stimuli differently. Critical differences may reside in the mean
strength of responses to visual stimuli, as reflected in bulk signals
detectable in fMRI, EEG or MEG studies, or may be more subtly composed of
differentiated activity of individual sensory neurons. Quantifying single-cell
Ca2+ responses to visual stimuli recorded with in vivo 2-photon imaging, we
found that visual detection correlates more strongly with population response
heterogeneity rather than overall response strength. Moreover, neuronal
populations showed consistencies in activation patterns across temporally
spaced trials in association with hit responses, but not during non-detections.
Contrary to models relying on temporally stable networks or bulk-signaling,
these results suggest that detection depends on transient differentiation in
neuronal activity within cortical populations.
