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Vestibulo-ocular Reflex:
Functional RoleCircuitry of Direct PathwaySystem Dynamics and Levels of Analysis
1) Neurons 2) Neural Circuits 3) Behavior
Functional Role of the Vestibulo-ocular Reflex
VOR GainOKN Gain
The Semicircular Canals: Rotational Movement Sensors
Hydrodynamic analysis of the canals predicted that the relationship between the angular displacement of the endolymph (ε(t)) and the head’s angular acceleration (α(t)) is:
θd ε2/dt2 + Π/dt + ∆ ε = θα(t)
Where: θ is the effective moment of inertia of the endolymph.
Π is a damping constant that reflects the viscous drag exerted by the canal wall as the endolymphflows past it, and
∆ Is a elastic restoring factor related
The dynamics of this equation are governed by two time constants,
1) a long one (τ1= Π / ∆ = 5s) and 2) a short one (τ2= θ / Π =.004s).
Calculated response to sinusoidal inputs of head velocity based of the torsion-pendulum model
θd ε2/dt2 + Π/dt + ∆ ε = θα(t)
Vestibular afferents response to “velocity trapezoid” inputs as predicted by the torsion-pendulum model
θd ε2/dt2 + Π/dt + ∆ ε = θα(t)
Dominant time constant is 5 s:
In contrast, the VOR has a time constant of ~20 s.
Two types of Hair cells
Type I characterized by calyx like endings of the sensory fibers.
Type II characterized by more conventional (bulbous) cell fiber synapses.
Regular Versus Irregular Afferents
- Spacing of action potentials
- Afferent gain and phase
- Efferent response magnitude
- Galvanic sensitivity
-Afferent innervation patterns type II haircells - regular afferents type I haircells - irregular affernts
Vestibular Nuclei: Inputs from the Labyrinth
Inputs:Superior/Medial
predominantly canalLateral
canal and otolithDescending
predominantly otolith
IV (plant transfer function)Fr = Ro + kE + rĖ
1 ms
1 ms1 ms
Horizontal Semicircular
Canal
H
+
ABD
I-PVP
Pathway delays
4 ms
Sinusoidal head perturbations: VOR dynamicshigher peak head velocities
A.
Gai
n
00.20.40.60.81.01.21.41.61.82.0
0 5 10 15 20 25 30Frequency (Hz)
B.
Phas
e (D
eg)
-80-60-40-20
020406080
0 5 10 15 20 25 30Frequency (Hz)
±271º/s±233º/s ±178º/s±154º/s
±150º/s±217º/s ±233º/s ±178º/s
±154º/s±150º/s
1 ms
1 ms1 ms
Horizontal Semicircular
Canal
H
+
ABD
I-PVP
Pathway delays
4 ms
Low versus High Frequency Rotations
Sadeghi and Cullen, in preparation
Low versus High Frequency Rotations
Sadeghi and Cullen, in preparation
PVP gain and phase response
Horizontal Semicircular
Canal
H
+
ABD
I-PVP
Intrinsic Membrane Properties
Serafin et al. 1991a,b
Postinhibitory Rebound Firing Correlates With Firing Rate Adaptation
Firing Rate Adaptation (FRA)
Sekirnjak and du Lac, 2002
Postinhibitory Rebound Firing (PRF)
Sekirnjak and du Lac, 2002
Sekirnjak and du Lac 2002