The Journal of Neurophysiology Vol. 82 No. 6 December 1999, pp. 3082-3094
Copyright ©1999 by the American Physiological Society
Visual Stimulus-Dependent Changes in Interhemispheric EEG
Coherence in Ferrets
D. C.
Kiper,1
M. G.
Knyazeva,1,2
L.
Tettoni,1 and
G. M.
Innocenti1,3
1Institut de Biologie Cellulaire et de
Morphologie, Université de Lausanne, 1005 Lausanne, Switzerland;
2Research Institute of Developmental Physiology,
119121 Pogodinskaya 8-2, Moscow, Russia; and
3Division of Neuroanatomy and Brain Development,
Department of Neuroscience, Karolinska Institutet, S-17177 Stockholm,
Sweden
Kiper, D. C.,
M. G. Knyazeva,
L. Tettoni, and
G. M. Innocenti.
Visual Stimulus-Dependent Changes in Interhemispheric EEG
Coherence in Ferrets. J. Neurophysiol. 82: 3082-3094, 1999. In recent years, the analysis of the coherence
between signals recorded from the scalp [electroencephalographic (EEG)
coherence] has been used to assess the functional properties of
cortico-cortical connections, both in animal models and in humans.
However, the experimental validation of this technique is still scarce.
Therefore we applied it to the study of the callosal connections
between the visual areas of the two hemispheres, because this
particular set of cortico-cortical connections can be activated in a
selective way by visual stimuli. Indeed, in primary and in low-order
secondary visual areas, callosal axons interconnect selectively
regions, which represent a narrow portion of the visual field
straddling the vertical meridian and, within these regions, neurons
that prefer the same stimulus orientation. Thus only isooriented
stimuli located near the vertical meridian are expected to change
interhemispheric coherence by activating callosal connections. Finally,
if such changes are found and are indeed mediated by callosal
connections, they should disappear after transection of the corpus
callosum. We perfomed experiments on seven paralyzed and anesthetized
ferrets, recording their cortical activity with epidural electrodes on areas 17/18, 19, and lateral suprasylvian, during different forms of
visual stimulation. As expected, we found that bilateral iso-oriented stimuli near the vertical meridian, or extending across it, caused a
significant increase in interhemispheric coherence in the EEG beta-gamma band. Stimuli with different orientations, stimuli located
far from the vertical meridian, as well as unilateral stimuli failed to
affect interhemispheric EEG coherence. The stimulus-induced increase in
coherence disappeared after surgical transection of the corpus
callosum. The results suggest that the activation of cortico-cortical
connections can indeed be revealed as a change in EEG coherence. The
latter can therefore be validly used to investigate the functionality
of cortico-cortical connections.
