Vestibulo-ocular Reflex: Functional Role Circuitry of ... III_ 05.pdf · Vestibulo-ocular Reflex: Functional Role Circuitry of Direct Pathway System Dynamics and Levels of Analysis

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