Expanding cortical dynamic range by coordinating input specific excitation with global inhibition

ANTONIA MARIN BURGIN; FREDERIC POIULLE; MASSIMO SCANZIANI

Cordoba

Congreso; I Reunion Conjunta de Neurociencias; 2009

Sociedad Argentina de Neurociencias

The cortex is sensitive to weak stimuli and responds to stronger inputs without saturating, but the mechanisms that enable this wide range of operation are not fully understood. We have addressed this issue in rat hippocampal slices where we monitored the progressive recruitment of CA1 pyramidal cells (PCs) in response to stimuli of increasing strength delivered to the Shaffer collaterals, their main excitatory afferent input. We found that recruitment of cortical neurons is staggered over a wide range of intensities because neurons activated by strong stimuli necessitate several-fold larger excitation to spike than neurons recruited by weaker inputs. Whereas the staggering results from an increase in widespread, basket cell-generated inhibition, the order of neuronal recruitment is set by local differences in afferent excitation. This mechanism drastically expands the dynamic range of distinct cortical populations without requiring changes in neuronal gain. Furthermore, it enables the recruitment of individual neurons at either the low or high end of the stimulus range, depending on the combination of active excitatory inputs.