PHASE-LOCKING OF NEURONAL RESPONSES TO THE VERTICAL REFRESH OF COMPUTER DISPLAY MONITORS IN CAT LATERAL GENICULATE-NUCLEUS AND STRIATE CORTEX

The proliferation of low-cost microcomputer systems has led to the use of these systems as alternatives to expensive display devices for vis ual physiology and psychophysics experiments. The video displays of th ese systems often lack the flexibility of achieving wide linear lumina nce ranges and high vertical refresh rates - two parameters which may influence data acquisition. We have examined the responses of neurons and pairs of neurons in cat LGN and striate cortex to bar and sinusoid al grating Stimuli generated by a conventional PC-based VGA graphics c ard and displayed on a NEC Multisync + color monitor with a 60 Hz vert ical (display) refresh rate. Responses to these stimuli were autocorre lated and power spectral densities (PSD) were calculated, revealing th at the majority of simple and complex cortical cells and nearly all LG N cells exhibited significant peaks in their autocorrelations at 16.7 ms and in the PSD at 60 Hz. Responses to identical stimuli generated w ith an optical bench using an incandescent light source contained no p ower at 60 Hz. Furthermore, cross-correlations between the spike train s of neuron-pairs were severely contaminated by peaks directly attribu table to the entrainment of the two elements of the pair to the vertic al refresh signal. Thus, we suggest that the use of conventional compu ter displays introduces a temporal artifact into neuronal spike trains in both single and multiple spike train analysis.