De. Wollman et La. Palmer, PHASE-LOCKING OF NEURONAL RESPONSES TO THE VERTICAL REFRESH OF COMPUTER DISPLAY MONITORS IN CAT LATERAL GENICULATE-NUCLEUS AND STRIATE CORTEX, Journal of neuroscience methods, 60(1-2), 1995, pp. 107-113
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.