Effect of stimulus intensity on the spike-local field potential relationship in the secondary somatosensory cortex

Supratim Ray, Steven S. Hsiao, Nathan E. Crone, Piotr J. Franaszczuk, Ernst Niebur

Research output: Contribution to journalArticlepeer-review


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 gammaoscillations, 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.

Original languageEnglish (US)
Pages (from-to)7334-7343
Number of pages10
JournalJournal of Neuroscience
Issue number29
StatePublished - Jul 16 2008


  • Gamma
  • High-gamma
  • Local field potential
  • Matching pursuit
  • Phase coding
  • Secondary somatosensory cortex

ASJC Scopus subject areas

  • Neuroscience(all)


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