Abstract Changes in neuronal firing were measured by intracellular and extracellular microelectrode recording during focal cooling of cat sensory motor cortex using a Peltier cooling device. Analysis was confined to neurons followed through cooling and rewarming back to normothermic levels. Rapidly cooling the cortex to temperature levels (19–21 C) were no unit activity could be recorded was associated with a steady decrease in firing frequency until silence, and a steady widening and lowering of amplitude of the action potential. Rapidly cooling the cortex to, and maintaining it at moderate temperature levels (27–29 C) was associated after 8–10 min with a brief period of high frequency repetitive firing (seizure) followed by silence until rewarming began. Burst activity was sometimes seen during rewarming. These findings were interpreted as suggesting that cooling to moderate temperature levels impeded the pump mechanisms exchanging Na and K across the neuron membrane. Further cooling to lower temperatures blocked the passive exchange of Na and K across membrane pores. These differential effects of cooling explain some of the variability in reports in the literature on the association between hypothermia and seizures.