Effects of x-irradiation on integrative patterns between EEG activity in different visual system structures was investigated in cats using the method of multiple spectral analysis. The statistical parameters studied were pair-wise coherence, multiple coherence, multiple coherence components, and multiple regression coefficients. Significantly high coherence, reflecting shared activity, was found between the activity in the visual cortex and the lateral geniculate or superior colliculus during photic stimulation but not prior to it. Strong linear activity relationships were found to a lesser extent between the visual cortex and the mesencephalic reticular formation and centre median. No mutual activity generally occurred between the hippocampus and the visual cortex. Four hundred roentgen head irradiation had a marked but transient effect on the coherence functions. The lateral geniculate had almost no linearly shared activity with the visual cortex from 1-4 hours post-irradiation. Other structures showed a decrease during this period. While in general no significant coherence levels were found individually with the various structures and the visual cortex, the optimum linear combination of activity as measured by multiple coherence did show a significant value at the flash frequency. Analysis of the components indicated a summing effect from essentially all of the structures other than the lateral geniculate.

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