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The Journal of Neuroscience, July 16, 2008, 28(29):7334-7343; doi:10.1523/JNEUROSCI.1588-08.2008

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Behavioral/Systems/Cognitive
Effect of Stimulus Intensity on the Spike–Local Field Potential Relationship in the Secondary Somatosensory Cortex

Supratim Ray,¹ Steven S. Hsiao,² Nathan E. Crone,³ Piotr J. Franaszczuk,³ and Ernst Niebur²

¹Department of Neurobiology, Harvard Medical School and Howard Hughes Medical Institute, Boston, Massachusetts 02115, ²Department of Neuroscience, Zanvyl Krieger Mind/Brain Institute, The Johns Hopkins University, Baltimore, Maryland 21218, and ³Department of Neurology, The Johns Hopkins Hospital, Baltimore, Maryland 21287-7247

Correspondence should be addressed to Supratim Ray, Department of Neurobiology, Harvard Medical School and the Howard Hughes Medical Institute, 201 Goldenson, 220 Longwood Avenue, Boston, MA 02115. Email: Supratim_Ray{at}hms.harvard.edu

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.

Key words: secondary somatosensory cortex; gamma; high-gamma; phase coding; local field potential; matching pursuit

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Received April 11, 2008; revised May 14, 2008; accepted June 4, 2008.

Correspondence should be addressed to Supratim Ray, Department of Neurobiology, Harvard Medical School and the Howard Hughes Medical Institute, 201 Goldenson, 220 Longwood Avenue, Boston, MA 02115. Email: Supratim_Ray{at}hms.harvard.edu

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				S. Ray, N. E. Crone, E. Niebur, P. J. Franaszczuk, and S. S. Hsiao Neural Correlates of High-Gamma Oscillations (60-200 Hz) in Macaque Local Field Potentials and Their Potential Implications in Electrocorticography J. Neurosci., November 5, 2008; 28(45): 11526 - 11536. [Abstract] [Full Text] [PDF]

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