Differential responsiveness of neocortical areas in the parieto- occipital
region to low-intensity stimulation in vitro.
Tobias Neumann-Haefelin, Georg Hagemann and Otto W. Witte.
Neurologische Klinik, Heinrich - Heine - Universit[umlaut]at, Moorenstr. 5,
APStracts 3:0070N, 1996.
SUMMARY AND CONCLUSIONS
1. Extracellular recording techniques were used to map the responses to low-
intensity stimuli across rat neocortical slices prepared from the parieto-
occipital region. Intracellular recordings were obtained in regions of
particular interest. Following electrophysiological recording, slices were
fixed in paraformaldehyde (4%) and Nissl-stained to allow identification of
cytoarchitectonically discrete areas. 2. In most neocortical areas of the
parieto-occipital region (Par1, HL, Fr1, Fr2), low-intensity stimuli applied
to layer V evoked only short monophasic fEPSPs in layer II/III. In Oc2
(secondary visual cortex, rostral part), however, a long-lasting potential (up
to 450 ms) consistently followed the short monophasic response seen in the
other areas. 3. The late response observed in Oc2 was characterized by its
inter-stimulus variability, polyphasic appearance and N-methyl-D-aspartate
(NMDA)-receptor dependence. Intracellular recordings obtained from layer
II/III pyramidal neurons located in Oc2 revealed short-latency, monophasic
early EPSPs followed by long-lasting EPSPs, which often triggered several
action potentials. 4. Recordings with two extracellular electrodes, one
positioned directly above the stimulation electrode and the other at a
variable distance (but also in layer II/III), suggested that the corresponding
excitation spreads across the slice, but does not cross the cytoarchitectonic
borders of Oc2. 5. Our data indicate that the electrophysiological responses
to low-intensity stimuli differ within the parieto-occipital region of the rat
neocortex. The type of response elicited depends on the cytoarchitectonic area
in which the stimulus is applied. The results raise the question of whether
further differences between neocortical subregions, with respect to basic
electrophysiological properties, exist.
Received 18 December 1995; accepted in final form 16 March 1996.
APS Manuscript Number J849-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96