Dipole source analyses of laser evoked potentials obtained from subdural grid recordings from primary somatic sensory cortex

The cortical potentials evoked by cutaneous application of a laser stimulus (laser evoked potentials, LEP) often include potentials in the primary somatic sensory cortex (S1), which may be located within the subdivisions of S1 including Brodmann areas 3A, 3B, 1, and 2. The precise location of the LEP generator may clarify the pattern of activation of human S1 by painful stimuli. We now test the hypothesis that the generators of the LEP are located in human Brodmann area 1 or 3A within S1. Local field potential (LFP) source analysis of the LEP was obtained from subdural grids over sensorimotor cortex in two patients undergoing epilepsy surgery. The relationship of LEP dipoles was compared wi…

Cutaneous Painful Laser Stimuli Evoke Responses Recorded Directly From Primary Somatosensory Cortex in Awake Humans

Negative and positive laser evoked potential (LEP) peaks (N2*, P2**) were simultaneously recorded from the primary somatosensory (SI), parasylvian, and medial frontal (MF: anterior cingulate and supplementary motor area) cortical surfaces through subdural electrodes implanted for the surgical treatment of intractable epilepsy. Distribution of the LEP N2*and P2**peaks was estimated to be in cortical areas (SI, parasylvian, and MF) identified by anatomic criteria, by their response to innocuous vibratory stimulation of a finger (v-SEP), and to electrical stimulation of the median nerve (e-SEP). The maximum of the LEP N2*peak was located on the CS, medial (dorsal) to the finger motor area, as …

Dipole Source Analyses of Early Median Nerve SEP Components Obtained From Subdural Grid Recordings

The median nerve N20 and P22 SEP components constitute the initial response of the primary somatosensory cortex to somatosensory stimulation of the upper extremity. Knowledge of the underlying generators is important both for basic understanding of the initial sequence of cortical activation and to identify landmarks for eloquent areas to spare in resection planning of cortex in epilepsy surgery. We now set out to localize the N20 and P22 using subdural grid recording with special emphasis on the question of the origin of P22: Brodmann area 4 versus area 1. Electroencephalographic dipole source analysis of the N20 and P22 responses obtained from subdural grids over the primary somatosensor…

Amplitudes of laser evoked potential recorded from primary somatosensory, parasylvian and medial frontal cortex are graded with stimulus intensity

Intensity encoding of painful stimuli in many brain regions has been suggested by imaging studies which cannot measure electrical activity of the brain directly. We have now examined the effect of laser stimulus intensity (three energy levels) on laser evoked potentials (LEPs) recorded directly from the human primary somatosensory (SI), parasylvian, and medial frontal cortical surfaces through subdural electrodes implanted for surgical treatment of medically intractable epilepsy. LEP N2* (early exogenous/stimulus-related potential) and LEP P2** (later endogenous potential) amplitudes were significantly related to the laser energy levels in all regions, although differences between regions w…

Attention to pain is processed at multiple cortical sites in man.

Painful cutaneous laser stimuli evoked potentials (LEPs) were recorded over the primary somatosensory (SI), parasylvian, and medial frontal (MF) cortex areas in a patient with subdural electrode grids located over these areas for surgical treatment of epilepsy. The amplitudes of the negative (N2*) and positive (P2**) LEP peaks over SI, parasylvian, and MF cortex were enhanced by attention to (counting stimuli), in comparison with distraction from the stimulus (reading for comprehension). Late positive deflections following the P2** peak (late potential—LP) were recorded over MF and from the lateral premotor regions during attention but not during distraction. These findings suggest that att…

Plasticity of pain-related neuronal activity in the human thalamus