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The Journal of Neurophysiology Vol. 83 No. 4 April 2000, pp. 2080-2092
Copyright ©2000 by the American Physiological Society
1Laboratory of Neurophysiology, School of Medicine, Université Catholique de Louvain, 1200 Brussels; and 2Center for Systems Engineering and Applied Mechanics, Université Catholique de Louvain, 1348 Louvain-la-Neuve, Belgium
Missal, M.,
S. de
Brouwer,
P. Lefèvre, and
E. Olivier.
Activity of Mesencephalic Vertical Burst Neurons During Saccades
and Smooth Pursuit. J. Neurophysiol. 83: 2080-2092, 2000. The activity of vertical burst neurons (BNs)
was recorded in the rostral interstitial nucleus of the medial
longitudinal fasciculus (riMLF-BNs) and in the interstitial nucleus of
Cajal (NIC-BNs) in head-restrained cats while performing saccades or
smooth pursuit. BNs emitted a high-frequency burst of action potentials
before and during vertical saccades. On average, these bursts led
saccade onset by 14 ± 4 ms (mean ± SD, n
= 23), and this value was in the range of latencies (~5-15
ms) of medium-lead burst neurons (MLBNs). All NIC-BNs (n
= 15) had a downward preferred direction, whereas riMLF-BNs
showed either a downward (n = 3) or an upward (n
= 5) preferred direction. We found significant correlations between saccade and burst parameters in all BNs: vertical amplitude was
correlated with the number of spikes, maximum vertical velocity with
maximum of the spike density, and saccade duration with burst duration.
A correlation was also found between instantaneous vertical velocity
and neuronal activity during saccades. During fixation, all riMLF-BNs
and ~50% of NIC-BNs (7/15) were silent. Among NIC-BNs active during
fixation (8/15), only two cells had an activity correlated with the eye
position in the orbit. During smooth pursuit, most riMLF-BNs were
silent (7/8), but all NIC-BNs showed an activity that was significantly
correlated with the eye velocity. This activity was unaltered during
temporary disappearance of the visual target, demonstrating that it was
not visual in origin. For a given neuron, its ON-direction
during smooth pursuit and saccades remained identical. The activity of
NIC-BNs during both saccades and smooth pursuit can be described by a
nonlinear exponential function using the velocity of the eye as
independent variable. We suggest that riMLF-BNs, which were not active
during smooth pursuit, are vertical MLBNs responsible for the
generation of vertical saccades. Because NIC-BNs discharged during both
saccades and pursuit, they cannot be regarded as MLBNs as usually
defined. NIC-BNs could, however, be the site of convergence of both the saccadic and smooth pursuit signals at the premotoneuronal level. Alternatively, NIC-BNs could participate in the integration of eye
velocity to eye position signals and represent input neurons to a
common integrator.
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