Our research is aimed at elucidating how ion channels regulate the processing of information by neurons in the cerebral cortex, i.e., the diverse mechanisms neurons use to convert synaptic input into action potentials. The proposed experiments will determine basic principles of how voltage-gated potassium (Kv) channels regulate postsynaptic processing of inputs in layer 5 (L5) neocortical pyramidal neurons (PNs). PNs are the output cells of cortex and key players in learning, memory, and sensorimotor processing, as well as the targets of central nervous system diseases (e.g., epilepsy). The proposed studies go beyond the standard notion that potassium channels act as an intrinsic brake on excitability. They are designed to determine the influence Kv2 and Kv7 channels have on the types of information that L5 PNs respond to and how that information is filtered before downstream transmission. We will study mechanisms controlling firing behavior in two classes of pyramidal neurons: intratelencephalic-projecting (IT) and pyramidal tract (PT) type, represented by two genetically-identified PNs with GFP expressed in populations of L5 PNs under control of unique genes: etv1 (IT) and thy1 (PT). We will test hypotheses concerning how Kv2 and Kv7 channels regulate burst firing (Aim 1) and continuous firing (repetitive bursting and suprathreshold resonance: Aim 2). Kv channel properties and expression are dynamic. They can undergo plastic changes in response to activity or signaling pathways and thus change neuronal filtering properties. Thus, we will also study use-dependent plasticity of intrinsic excitability (Aim 3). We use transgenic mouse lines and state-of-the-art electrophysiological approaches, including somatic / dendritic paired recordings, dynamic clamp, internal pipet perfusion, nucleated patch and on-cell patch recordings, as well as whole cell and gramicidin perforated patch. We also use two-photon and charge-coupled device (CCD)-based Ca2+ imaging systems. Our stimulus protocols are designed to mimic natural synaptic activity arriving at the soma of a neuron (the common summing point for all dendrites) and will be systematically varied to simulate different levels or composition of inputs. Our findings will have major implications for cortical processing, ion channel function, understanding neural computations, and mechanisms underlying epilepsy, anesthesia, learning and memory.