Neural spike irregularity in adjacent cells of the same visual cortical column are unrelated despite other shared properties

Reliable visual information processing is required for coordinated visuomotor behavior. Yet, in visual cortical neurons, repeated presentation of optimal visual stimuli frequently fail to elicit output spike trains that show temporal precision from trial to trial except in the average spike rate, spawning the belief that a population of neurons is required to provide, on average, the required reliability. If so, neighboring cells in a cortical column that share common anatomical inputs and show similar physiological response characteristics to visual stimuli, such as orientation preference, may be expected to show similar degrees of irregularity in the inter spike interval (ISI). We measured ISI irregularity by computing the *coefficient of variation in two adjacent cells simultaneously in the cat primary visual cortex (*CV = standard deviation in the ISI/ mean ISI in a response window). Cats were initially anaesthetized (ketamine 15mg/kg and xylazine 3mg/kg mixture, i.m.) and then maintained on 70/30% N2O/O2 gaseous mixture and sodium pentobarbitone (1-1.5 mg/kg/hr, i.v.) with gallamine triethiodide (10mg/kg/hr, i.v.) for paralysis. We compared CVs from pairs of cells recorded from the same electrode (isolated with Spike2 software CED) that responded to the same stimuli over the same temporal window. Over a large number of trials, no significant correlation occurred between CVs for each cell. That is, in the common inputs to adjacent cells, there are enough random synaptic failures and variations in the sites of synaptic contact to explain the lack of correlation in their irregular firing.