Abstract
Variability in neuronal response latency has been typically considered caused by random noise. Previous studies of single cells and large neuronal populations have shown that the temporal variability tends to increase along the visual pathway. Inspired by these previous studies, we hypothesized that functional areas at later stages in the visual pathway of face processing would have larger variability in the response latency. To test this hypothesis, we used magnetoencephalographic data collected when subjects were presented with images of human faces. Faces are known to elicit a sequence of activity from the primary visual cortex to the fusiform gyrus. Our results revealed that the fusiform gyrus showed larger variability in the response latency compared to the calcarine fissure. Dynamic and spectral analyses of the latency variability indicated that the response latency in the fusiform gyrus was more variable than in the calcarine fissure between 70 ms and 200 ms after the stimulus onset and between 4 Hz and 40 Hz, respectively. The sequential processing of face information from the calcarine sulcus to the fusiform sulcus was more reliably detected based on sizes of the response variability than instants of the maximal response peaks. With two areas in the ventral visual pathway, we show that the variability in response latency across brain areas can be used to infer the sequence of cortical activity.
Highlights
Neural variability in response latency is usually considered to be caused by random noise
It has been shown that neural responses differ across trials when the identical stimulus is presented repeatedly: at the neuronal level, single-digit unit recordings suggested that neuronal responses to the identical visual stimuli varied considerably across trials in cat and monkey visual cortex[9,10,11]
Evoked responses to images of faces were observed in the calcarine fissure and fusiform gyrus in both the left and right hemispheres
Summary
Neural variability in response latency is usually considered to be caused by random noise. The sequence of brain activity across areas has been typically inferred by the relative size of a specific feature of the evoked responses Temporal features, such as onset or time-to-peak, have been widely used to estimate the progression of cortical activity. Based on micro- and macro-scale neuronal findings in the visual cortex, we hypothesized that functional areas at later processing stages would have larger variability in response latency compared to areas at earlier processing stages To test this hypothesis of increasing latency variability along the functional pathway, we examined if the size of regional latency variability would match the known sequence of cortical processing. We used the ventral pathway of face processing to test this hypothesis
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