Signal characteristics of visual cortex and lateral geniculate during contralateral and ipsilateral photic stimulation

Abstract

1. 1. Frequency-specific outputs from the visual cortex and lateral geniculate of unanesthetized rats were recorded and measured by means of matched narrow bandpass filters under conditions of no stimulation and bandpass-tuned flicker stimulation at the contralateral and ipsilateral eye. 2. 2. In the visual cortex, output was significantly higher under stimulation than during the resting condition, and output under contralateral stimulation was significantly higher than under ipsilateral stimulation. 3. 3. Signal-to-noise levels in the visual cortex were computed for both contralateral and ipsilateral stimulation. It was found that a S/ N advantage of 4.38:1 favored contralateral stimulation over ipsilateral stimulation, whereas contralateral stimulation was approximately 13 times as effective as ipsilateralv with respect to the signal-to-noise power ratio. 4. 4. Stimulation resulted in a significant increase in the duration of modulation periods at the visual cortex. The observed shift in modulation periods from rest to stimulation was significantly greater for contralateral stimulation compared to ipsilateral stimulation. 5. 5. In the lateral geniculate, output was significantly higher under stimulation than during the resting condition, and as with the visual cortex, output under contralateral stimulation was significantly higher than under ipsilateral stimulation. 6. 6. Signal-to-noise levels in the lateral geniculate showed as S/ N advantage of 4.15:1 for contralateral over ipsilateral stimulation, whereas contralateral stimulation was approximately 10 times as effective as ipsilateral with respect to the signal-to-noise power ratio. 7. 7. At the lateral genicualte, contralateral stimulation resulted in a significant increase in modulation period, whereas ipsilateral stimulation yielded practically no increase. 8. 8. As the photo-evoked signal passed from lateral geniculate to visual cortex, S/ N improved by a factor of approximately four, and the signal-to-noise power ratio by a factor of approximately ten. 9. 9. The endogenous modulation period was significantly longer in the visual cortex than in the lateral geniculate. This was true under either contralateral or ipsilateral stimulation. 10. 10. The known ratio of decussating optic nerve fibers in the rat was quantitatively reflected in corresponding relative signal-to-noise power ratios for contralateral and ipsilateral stimulation. This was true at both the occipital cortex and the lateral geniculate. 11. 11. Modulation-period distributions in the visual cortex and lateral geniculate corresponded very well with theoretically predicted distributions derived from a proposed mathematical model.