Optical tools present new opportunities for studying the relationship between neural circuitry and function. Using fluorescent neuronal tracing together with in vivo two-photon calcium imaging, we tested whether neurons in ferret primary visual cortex that project to dorsal vs. ventral visual stream areas differ accordingly in their physiological responses to visual stimuli. We injected two different colored tracers (Cholera Toxin B conjugated to Alexa Fluor 555 and 594), one into Posterior Suprasylvian Sulcus, or ‘PSS’, the probable analog of primate dorsal stream area MT, and one into Area 21, the probable analog of primate ventral stream area V4. After neurons in V1 were retrogradely filled (4-10 days after the injection), we implanted a cranial window over V1, loaded a region containing both sets of retrogradely labeled cells with the calcium indicator dye Oregon Green-BAPTA, and characterized their activity in response to visual stimuli using 2-photon imaging. Using improved signal extraction methods to obtain tuning curves from the raw fluorescence time series (see Malik et al., this session), we found that V1 neurons projecting to PSS are more direction-selective than neurons projecting to Area 21, but that the two cell groups do not differ in their orientation selectivity. This difference in direction selectivity also exists within individual imaging sessions, when both sets of projection neurons are imaged simultaneously from the same ~250x250 um window. Additionally, we found that neurons projecting to PSS prefer shorter bars than neurons projecting to Area 21, i.e., PSS-projecting cells show behavior consistent with end-stopping (end-inhibition), whereas Area 21-projecting cells show behavior consistent with length summation. This difference also holds within individual imaging sessions. We also confirmed our previous finding that V1 neurons projecting to PSS prefer higher temporal frequencies (TF) and lower spatial frequencies (SF) than neurons projecting to Area 21, though this was true only within individual imaging sessions, not when all cells across all sessions were treated as independent samples. The existence of such ‘sorting’ of outputs from V1 into the dorsal and ventral streams might help constrain possible explanations for how functional modularity arises in higher-order visual areas.

Society for Neuroscience Abstract, 2009.