title: Effect of stimulus intensity on the spike-local field potential relationship in the secondary somatosensory cortex.
abstract: Neuronal oscillations in the gamma frequency range have been reported in many cortical areas, but the role they play in cortical processing remains unclear. We tested a recently proposed hypothesis that the intensity of sensory input is coded in the timing of action potentials relative to the phase of gamma oscillations, thus converting amplitude information to a temporal code. We recorded spikes and local field potential (LFP) from secondary somatosensory (SII) cortex in awake monkeys while presenting a vibratory stimulus at different amplitudes. We developed a novel technique based on matching pursuit to study the interaction between the highly transient gamma oscillations and spikes with high time-frequency resolution. We found that spikes were weakly coupled to LFP oscillations in the gamma frequency range (40-80 Hz), and strongly coupled to oscillations in higher gamma frequencies. However, the phase relationship of neither low-gamma nor high-gamma oscillations changed with stimulus intensity, even with a 10-fold increase. We conclude that, in SII, gamma oscillations are synchronized with spikes, but their phase does not vary with stimulus intensity. Furthermore, high-gamma oscillations (>60 Hz) appear to be closely linked to the occurrence of action potentials, suggesting that LFP high-gamma power could be a sensitive index of the population firing rate near the microelectrode.
authors.affiliation: Department of Neurobiology, Harvard Medical School and Howard Hughes Medical Institute, Boston, Massachusetts 02115, USA. Supratim_Ray@hms.harvard.edu
authors.forename: Supratim
authors.initials: S
authors.lastname: Ray
authors.forename: Steven S
authors.initials: SS
authors.lastname: Hsiao
authors.forename: Nathan E
authors.initials: NE
authors.lastname: Crone
authors.forename: Piotr J
authors.initials: PJ
authors.lastname: Franaszczuk
authors.forename: Ernst
authors.initials: E
authors.lastname: Niebur
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D008253:Macaca mulatta; D008297:Male; D010812:Physical Stimulation / Q000379:methods; D013003:Somatosensory Cortex / Q000502:physiology*; D014732:Vibration