Haemodynamic responses to radial motion in the visual cortex

Sobanawartiny Wijeakumar, Uma Shahani, William A. Simpson, Daphne McCulloch

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Abstract

Functional near-infrared spectroscopy (fNIRS) is an optical imaging technique that relies on emitting near-infrared light into cortical tissue to measure changes in haemoglobin concentrations as a result of stimulation. The purpose of this study was to observe haemodynamic changes in response to moving stimuli over the primary visual cortex. The test stimuli were radially expanding and contracting concentric gratings and the control stimulus was a matched stationary pattern. A two-channel oximeter (Oxiplex TS) was
used to record changes in oxyhaemoglobin (HbO), de-oxyhaemoglobin (Hb) and total haemoglobin concentrations (THb). An increase in
haemodynamic activation was observed 20 s after the onset of motion and maintained for up to 20 s following motion offset (30 s time
window). This was compared to a time window of 10 s before the offset of the stationary presentation. Differences between expanding
and contracting motion did not achieve significance at any of the locations. However, a significantly larger HbO response was observed
across the 30 s time window when compared to the baseline window at both occipital locations. Preliminary results from more temporal
locations also showed a similar trend. It is suggested that the delayed rise in HbO levels could be due to an inconsistent maintenance
of luminance and contrast-related features of the moving stimuli in V1 receptive fields. Furthermore, motion-after effects could have
contributed to delaying the drop to baseline levels. The current study has shown some evidence that fNIRS can be used to record
haemodynamic responses to moving stimuli from the visual cortex. We suggest that longer durations of randomised moving, stationary
and grey screen presentations would be useful in teasing apart pure motion responses and after-effects. fNIRS could also potentially be
used to investigate haemodynamic changes in disorders such as amblyopia that present with motion processing deficits.
Original languageEnglish
Pages (from-to)231-236
Number of pages6
JournalJournal of Near Infrared Spectroscopy
Volume21
Issue number4
DOIs
Publication statusPublished - 12 Aug 2013

Keywords

  • fNIRS
  • motion
  • visual cortex
  • imaging

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