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Responses to Efferent Activation and Excitatory Response-Intensity Relations of Turtle Posterior-Crista Afferents
Departments of 1 Surgery (Otolaryngology-Head and Neck Surgery) and 2 Neurobiology, Pharmacology and Physiology, University of Chicago, Chicago, Illinois 60637 Brichta, Alan M. and Jay M. Goldberg. Responses to Efferent Activation and Excitatory Response-Intensity Relations of Turtle Posterior-C...
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Published in: | Journal of neurophysiology 2000-03, Vol.83 (3), p.1224-1242 |
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Main Authors: | , |
Format: | Article |
Language: | English |
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Online Access: | Get full text |
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Summary: | Departments of 1 Surgery (Otolaryngology-Head
and Neck Surgery) and 2 Neurobiology,
Pharmacology and Physiology, University of Chicago, Chicago, Illinois
60637
Brichta, Alan M. and
Jay M. Goldberg.
Responses to Efferent Activation and Excitatory
Response-Intensity Relations of Turtle Posterior-Crista
Afferents. J. Neurophysiol. 83: 1224-1242, 2000. Multivariate
statistical formulas were used to infer the morphological type and
longitudinal position of extracellularly recorded afferents. Efferent
fibers were stimulated electrically in the nerve branch interconnecting
the anterior and posterior VIIIth nerves. Responses of bouton (B) units
depended on their inferred position: BP units (near the planum
semilunatum) showed small excitatory responses; BT units (near the
torus) were inhibited; BM units (in an intermediate position) had a
mixed response, including an initial inhibition and a delayed
excitation. Calyx-bearing (CD-high) units with an appreciable
background discharge showed large per-train excitatory responses
followed by smaller post-train responses that could outlast the shock
train by 100 s. Excitatory responses were smaller in calyx-bearing
(CD-low) units having little or no background activity than in CD-high
units. Excitatory response-intensity functions, derived from the
discharge during 2-s angular-velocity ramps varying in intensity, were
fit by empirical functions that gave estimates of the maximal response
( r MAX ), a threshold velocity
( v T ), and the velocity producing a
half-maximal response ( v 1/2 ). Linear gain is
equal to r MAX / v S ,
v S = v 1/2 v T .
v S provides a measure of the velocity range
over which the response is nearly linear. For B units,
r MAX declines by as much as twofold over the
2-s ramp, whereas for CD units, r MAX
increases by 15% during the same time period. At the end of the ramp,
r MAX is on average twice as high in CD as in
B units. Thresholds are negligible in most spontaneously active units,
including almost all B and CD-high units. Silent CD-low units typically
have thresholds of 10-100 deg/s. BT units have very high linear gains
and v S < 10 deg/s. Linear gains are
considerably lower in BP units and v S > 150 deg/s. CD-high units have intermediate gains and near 100 deg/s
v S values. CD-low units have low gains and
v S values ranging from 150 to more than 300 deg/s. The results suggest that BT units are designed to measure the
small head movements involved in postural control, whereas BP a |
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ISSN: | 0022-3077 1522-1598 |
DOI: | 10.1152/jn.2000.83.3.1224 |