Functional properties and interactions of neuron pairs simultaneously recorded in the medial geniculate body of the cat.

Pairs of single units were recorded simultaneously from the same microelectrode in the medial geniculate body (MGB) of nitrous oxide anaesthetized cats. Crosscorrelation histograms of each spike train pairs were computed and distributed in five main classes, interpreted in terms of functional interaction between neighbouring neurons. Overall 40% of the 950 recorded pairs showed independent firing during spontaneous activity. Histogram shapes suggestive of simple functional connectivity were found in 38% of the pairs: common inputs (20%), excitatory (15%) and inhibitory (3%) synaptic links. Complex and 'borderline' histogram shapes made up the rest of the sample (22%). Subdivisions of the MGB had the same types and proportions of interaction classes. Several of these interactions showed, in statistical terms only, preferential associations with some other descriptive features of neuronal behaviour: pattern of spontaneous firing, sensitivity to acoustic stimuli, and to a lesser extent characteristic frequency, response latency, response pattern and width of the response range. Simultaneous recording of nearby neuron pairs allowed to test if a given functional property is spatially organized or randomly distributed in the MGB. Response latency, width of the response range behaved as if randomly distributed, whereas binaural interactions and characteristic frequency as if spatially organized.