Cortical excitability and the shape of the haemodynamic response

Abstract

Individual differences in the temporal dynamics of the haemodynamic response can reflect cortical excitation and can reveal underlying cortical physiology. Here, we show differences in the shape of the haemodynamic response that are dependent on stimulus parameters. Two sets of visual stimuli were used varying in parameters that are known to manipulate the haemodynamic response in the visual cortex. We measured the oxyhaemoglobin response using near infrared spectroscopy. The first set of stimuli comprised chromatic square-wave gratings that varied with respect to the separation in the CIE UCS chromaticities of the alternating bars. The gratings with large separations in chromaticity evoked an oxyhaemoglobin response with greater amplitude, consistent with greater activation of the visual cortex. The second set of stimuli comprised horizontal achromatic gratings that (1) were static, (2) drifted at a constant velocity towards fixation, or (3) reversed direction every half spatial cycle to create a vertical vibrating motion. Although the three types of grating had a similar effect on the amplitude of the oxyhaemoglobin response, the moving gratings (2 and 3) evoked a steeper decrease in oxyhaemoglobin concentration after stimulus-offset. The steeper slope appears to reflect the poststimulus undershoot and the slope may provide a correlate of cortical excitability when the amplitude of the haemodynamic response has saturated.

Hemodynamic response function abnormalities in schizophrenia during a multisensory detection task

“…In summary, during a simple multisensory detection task, SP exhibited abnormal PSU after normal task‐related activation in secondary unisensory areas, as well as abnormal task‐induced deactivation in the aDMN, and the two hemodynamic abnormalities were related. Current results are consistent with the view that separate neural processes underlie the two phases of the HRF [Haigh et al, ; Mullinger et al, ; Sadaghiani et al, ] and that they are differentially affected in SP. Such findings do not directly contradict the large body of literature on evoked BOLD responses in SP that used a single parameter to estimate the HRF.…”

“…Collectively, current results are consistent with the view that separate neural processes underlie the two phases of the HRF [Haigh et al, ; Mullinger et al, ; Sadaghiani et al, ], and that they are differentially affected in SP (Supporting Information Fig. S1).…”

Cortical Hyper‐Excitability in Migraine in Response to Chromatic Patterns

“…The increase in visual discomfort with larger chromaticity separations replicated previous findings, 21 which demonstrated that, regardless of the color pairs used, chromaticity separation accounted for the majority of the variance in visual discomfort ratings. Similarly, larger neural responses to larger chromaticity separations is consistent with previous reports of increased hemodynamic responses 21,28 and greater alpha suppression 20 in visual cortex. Together, this suggests that the visual system is sensitive to chrominance as well as luminance, and that greater chrominance produces a large neural response which is consistent with increasing cortical excitation.…”

Steady‐state VEP responses to uncomfortable stimuli

“…If this is true, uncomfortable stimuli should produce an increased response compared to comfortable stimuli. There is evidence that discomfort from gratings is related to the haemodynamic brain response, for both black and white (Coutts et al ., ) and chromatic gratings (Haigh et al ., , ). There is also some evidence for increased visual evoked potentials on viewing black‐and‐white riloid stimuli: stimuli that were most comfortable were also those with a lower event‐related potential (ERP) response amplitude, specifically the P100 response (O'Hare et al ., ).…”