title: The temporal frequency tuning of human visual cortex investigated using synthetic aperture magnetometry.
abstract: Using synthetic aperture magnetometry (SAM) analyses of magnetoencephalographic (MEG) data, we investigated the variation in cortical response magnitude and frequency as a function of stimulus temporal frequency. In two separate experiments, a reversing checkerboard stimulus was used in the right or left lower visual field at frequencies from 0 to 21 Hz. Average temporal frequency tuning curves were constructed for regions-of-interest located within medial visual cortex and V5/MT. In medial visual cortex, it was found that both the frequency and magnitude of the steady-state response varied as a function of the stimulus frequency, with multiple harmonics of the stimulus frequency being found in the response. The maximum fundamental response was found at a stimulus frequency of 8 Hz, whilst the maximum broadband response occurred at 4 Hz. In contrast, the magnitude and frequency content of the evoked onset response showed no dependency on stimulus frequency. Whilst medial visual cortex showed a power increase during stimulation, extra-striate areas such as V5/MT exhibited a bilateral event-related desynchronisation (ERD). The frequency content of this ERD did not depend on the stimulus frequency but was a broadband power reduction across the 5-20 Hz frequency range. The magnitude of this ERD within V5/MT was strongly low-pass tuned for stimulus frequency, and showed only a moderate preference for stimuli in the contralateral visual field.
authors.affiliation: The Wellcome Trust Laboratory for MEG studies, Neurosciences Research Institute, Aston University, Birmingham B4 7ET, UK.
authors.forename: Ian P
authors.initials: IP
authors.lastname: Fawcett
authors.forename: Gareth R
authors.initials: GR
authors.lastname: Barnes
authors.forename: Arjan
authors.initials: A
authors.lastname: Hillebrand
authors.forename: Krish D
authors.initials: KD
authors.lastname: Singh
mesh_terms: D000328:Adult; D001931:Brain Mapping; D003344:Cortical Synchronization; D004292:Dominance, Cerebral / Q000502:physiology; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D015225:Magnetoencephalography; D008297:Male; D009415:Nerve Net / Q000502:physiology; D009949:Orientation / Q000502:physiology; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013998:Time Perception / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology