Local Integration Accounts for Weak Selectivity of Mouse Neocortical Parvalbumin Interneurons
Dissecting the functional roles of excitatory and inhibitory neurons in cortical circuits is a fundamental goal in neuroscience. Of particular interest are their roles in emergent cortical computations such as binocular integration in primary visual cortex (V1). We measured the binocular response selectivity of genetically defined subpopulations of excitatory and inhibitory neurons. Parvalbumin (PV+) interneurons received strong inputs from both eyes but lacked selectivity for binocular disparity. Because broad selectivity could result from heterogeneous synaptic input from neighboring neurons, we examined how individual PV+ interneuron selectivity compared to that of the local neuronal network, which is primarily composed of excitatory neurons. PV+ neurons showed functional similarity to neighboring neuronal populations over spatial distances resembling measurements of synaptic connectivity. On the other hand, excitatory neurons expressing CaMKIIα displayed no such functional similarity with the neighboring population. Our findings suggest that broad selectivity of PV+ interneurons results from nonspecific integration within local networks. [read more]
Marmoset Tracking
We characterized visual motion dependence of smooth eye movement in marmosets trained to perform fixation tasks. We found that marmosets naturally pursue small moving targets with some degree of diligence without any further demands on their behavioral conditioning other than their initial fixation training. As seen in other primates, we find that initial pursuit is driven by the direction of target motion, with acceleration amplitude related to the target velocity. Furthermore, we find that eye movements evoked by small perturbations in target velocity are larger during pursuit than from fixation, indicating that distinct modes exist for tracking targets. These features resemble those of macaques and humans, although marmosets do complete much fewer trials than is typical of a highly trained macaque. We conclude that the marmoset does exhibit the pursuit behavior naturally and thus may provide a complementary model system in which to study the natural sensory-motor transformations involved in smooth pursuit. [read more]
Eye-Tracking and Intracellular, Whole-Cell, Current-Clamp Measurements of V1 Neurons
Continuous whole cell current clamp record of Vm from a V1 neuron and eye movements in a behaving primate viewing sinusoidal drifting grating visual stimuli over multiple trials and inter-trial periods. [read more]