Antidromic activation, spike duration, and spike-triggered averaging of axonal, synaptic, and dendritic events: Multiple tools for in vivo identification of diverse neocortical cell classes
Harvey A. Swadlow Department of Psychology The University of Connecticut
Understanding neocortical function will require insight into the nature of the parallel streams of information that are conveyed to multiple targets of the cortex by distinct efferent pathways and, more generally, into the different modes of information processing that are implemented by the diversity of excitatory and inhibitory cortical cell types that constitute the cortical network. Whereas in vivo extracellular studies often yield functional categories of cortical neurons that are based on task/stimulus-related response properties, it is often not known how such functional classes fit into well-established neuronal classification schemes. Converging evidence from multiple cortical regions and animal models shows that morphologically or biophysically distinct cell classes can differ greatly in measures of stimulus or task-related information processing and in baseline activity. Fast-spike inhibitory interneurons differ from excitatory pyramidal neurons, and different classes of pyramidal neurons, projecting their axons to diverse targets of the cortex, differ radically among themselves. Extracellular single-unit analyses aimed at understanding task-related response properties can, therefore, be enriched considerably by knowledge of the cell-types under study. One way to achieve this is to identify physiological "signatures" that characterize distinct cell classes. My talk will focus on two such signatures, antidromic activation and extracellular spike duration, on the errors that are associated with these signatures (false positives, false negatives, and sampling biases), and on procedures for reducing these errors. I will also discuss other tools for identifying distinct cortical and thalamic cell classes, including spike-triggered averaging of axonal, synaptic and dendritic events.
