Physiological differences between neurons in layer 2 and layer 3 of primary visual cortex (V1) of alert macaque monkeys.

Gur M, Snodderly DM.
J Physiol. 2008 Mar 6

The physiological literature does not distinguish between the superficial layers 2 and 3 of primary visual cortex even though these two layers differ in their cytoarchitecture and anatomical connections. To distinguish layer 2 from layer 3, we have analyzed the response characteristics of neurons recorded during microelectrode penetrations perpendicular to the cortical surface. Extracellular responses of single neurons to sweeping bars were recorded while macaque monkeys performed a fixation task. Data were analyzed from penetrations where cells could be localized to specific depths in the cortex. Although the most superficial cells (depth: 145-371 microm; presumably layer 2) responded preferentially to particular stimulus orientations, they were less selective than cells encountered immediately beneath them (depth: 386-696 microm; presumably layer 3). Layer 2 cells had smaller spikes, higher levels of ongoing activity, larger receptive field activating regions, and less finely tuned selectivity for stimulus orientation and length than layer 3 cells. Direction selectivity was found only in layer 3. These data suggest that layer 3 is involved in generating and transmitting precise, localized information about image features, while the lesser selectivity of layer 2 cells may reflect more global processing or top-down modulation of V1 by feedback from higher cortical areas.

PMID: 18325976

Fulltext: http://jp.physoc.org/cgi/rapidpdf/jphysiol.2008.151795v1