title: Transcranial Magnetic Stimulation Changes Response Selectivity of Neurons in the Visual Cortex.
abstract: BACKGROUND
  Transcranial magnetic stimulation (TMS) is used to selectively alter neuronal activity of specific regions in the cerebral cortex. TMS is reported to induce either transient disruption or enhancement of different neural functions. However, its effects on tuning properties of sensory neurons have not been studied quantitatively.
  
  
  OBJECTIVE
  Here, we use specific TMS application parameters to determine how they may alter tuning characteristics (orientation, spatial frequency, and contrast sensitivity) of single neurons in the cat's visual cortex.
  
  
  METHODS
  Single unit spikes were recorded with tungsten microelectrodes from the visual cortex of anesthetized and paralyzed cats (12 males). Repetitive TMS (4 Hz, 4 s) was delivered with a 70 mm figure-8 coil. We quantified basic tuning parameters of individual neurons for each pre- and post-TMS condition. The statistical significance of changes for each tuning parameter between the two conditions was evaluated with a Wilcoxon signed-rank test.
  
  
  RESULTS
  We generally find long-lasting suppression which persists well beyond the stimulation period. Pre- and post-TMS orientation tuning curves show constant peak values. However, strong suppression at non-preferred orientations tends to narrow the widths of tuning curves. Spatial frequency tuning exhibits an asymmetric change in overall shape, which results in an emphasis on higher frequencies. Contrast tuning curves show nonlinear changes consistent with a gain control mechanism.
  
  
  CONCLUSIONS
  These findings suggest that TMS causes extended interruption of the balance between sub-cortical and intra-cortical inputs.
authors: Vision Science Graduate Group, School of Optometry, University of California, Berkeley, CA 94720, USA.
authors: Taekjun
authors: T
authors: Kim
authors: Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, USA.
authors: Elena A
authors: EA
authors: Allen
authors: Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, USA.
authors: Brian N
authors: BN
authors: Pasley
authors: Vision Science Graduate Group, School of Optometry, University of California, Berkeley, CA 94720, USA; Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, USA. Electronic address: rfreeman@berkeley.edu.
authors: Ralph D
authors: RD
authors: Freeman
mesh_terms: D000818:Animals; D002415:Cats; D015350:Contrast Sensitivity; D008297:Male; D008839:Microelectrodes; D009475:Neurons, Afferent / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D014793:Visual Cortex / Q000166:cytology* / Q000502:physiology
keywords: Contrast selectivity; Orientation; Single unit activity; Spatial frequency; Transcranial magnetic stimulation