Ectopic axonal firing in an epileptic cortical focus is not triggered by thalamocortical volleys during the interictal stage

Brett, Barbara and Daniel S. Barth. Subcortical modulation of high-frequency (gamma band) oscillating potentials in auditory cortex. J. Neurophysiol. 78: 573–581, 1997. The purpose of this study was to use depth electrical stimulation and retrograde horseradish peroxidase (HRP) labeling to determine what role certain subcortical nuclei play in the neurogenesis of high-frequency gamma (∼40 Hz) oscillations in rat auditory cortex. Evoked and spontaneous electrocortical oscillations were recorded with the use of a high-spatial-resolution multichannel epipial electrode array while electrical stimulation was delivered to the posterior intralaminar (PIL) region of the ventral acoustic thalamus and to the centrolateral nucleus (CL) and the nucleus basalis (NB), which have been previously implicated in the production of cortical gamma oscillations. PIL stimulation consistently evoked gamma oscillations confined to a location between primary and secondary auditory cortex, corresponding to the region where spontaneous gamma oscillations were also recorded. Stimulation of the CL and NB did not evoke gamma oscillations in auditory cortex. HRP placed in the cortical focus of evoked gamma oscillations labeled cell bodies in the PIL, and in more lateral regions of the ventral acoustic thalamus, which on subsequent stimulation also evoked gamma oscillations in auditory cortex. No cells were labeled in either the CL or NB. These results indicate that the PIL and the lateral regions of ventral acoustic thalamus provide anatomically distinct input to auditory cortex and may play an exclusive and modality-specific role in modulating gamma oscillations in the auditory system.

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Somatotopic projections of mystacial vibrissae on cerebral cortex of cats

Journal of Neurophysiology ◽

10.1152/jn.1977.40.5.997 ◽

1977 ◽

Vol 40 (5) ◽

pp. 997-1014 ◽

Cited By ~ 22

Author(s):

R. W. Dykes ◽

J. D. Dudar ◽

D. G. Tanji ◽

N. G. Publicover

Keyword(s):

Cerebral Cortex ◽

Evoked Potential ◽

Skin Surface ◽

Areal Extent ◽

Negative Peak ◽

Stimulus Parameters ◽

Positive Peak ◽

Mystacial Vibrissae ◽

Cortical Map ◽

Cortical Focus

1. Using classical evoked-potential techniques and 100-micron deflections of one vibrissa, at least three loci of potentials were identified in cats' cortices. 2. The relationships of these loci to cortical landmarks and to each other varied sufficiently to prevent specification of homologies between animals. 3. Attempts to differentiate the loci on functional criteria were unsuccessful. The areal extent of each locus appeared similar and there was evidence of a specific somatotopic pattern within each locus; in each locus different vibrissae were represented at different cortical points. 4. Latencies differed slightly between the loci, being shortest at the most rostral site and longest at the caudal site. In all loci, off-center latencies were longer, but this difference was detected only after complete maps of all three loci were produced. 5. The focus of potentials for an individual vibrissa was radically different, depending on the parameter measured (negative peak, positive peak, and latency). The focus of potentials could also be shifted by changing the velocity or direction of the stimulus. 6. The effects of these stimulus parameters on the cortical map suggest that a cortical focus represents more than simply a point on the skin surface.

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