Natural and drug-induced variations of velocity and duration of human saccadic eye movements: Evidence for a control of the neural pulse generator by local feedback

Abstract

The present report considers goal directed human saccadic eye movements. It addresses the question how a given perceived target excentricity is transformed into the innervation pattern that creates the saccade to the target. More specifically, it investigates whether this pattern is an appropriately selected preprogram or whether it is continuously controlled by a local feedback loop that compares a non-visual eye position signal to the perceived target excentricity (a visual signal would be too slow). To this end, the relation between the accuracy of saccades aimed at a given target and their velocity and duration was examined. Duration and velocity were found to vary by as much as 60% while the amplitude showed no related variation and had an almost constant accuracy of about 90%. By administrating diazepam, the variabiity of saccade duration and velocity could be further increased, but still the amplitude remained almost constant. These results favour the hypothesis that saccadic innervation is controlled by a local feedback loop.

A neural model of the saccade generator in the reticular formation

“…The LLBNs in the present SG model are not assumed to be perfect or near perfect integrators, as in the Scudder model, since this assumption is not supported in the data (Raybourn and Keller, 1977). We also do not need to hypothesize a separate resetable integrator cell type, as in Jurgens et al (1981), since in the FOVEATE model, the EBN functions as a resetable integrator that is reset by the OPN. In contrast to the Dominey and Arbib (1991) The model does not include all known connections, since these are not rate-limiting in simulating the targeted data.…”

“…This is a part of the brain that invites, indeed requires, models in order to be understood, and many models (e.g. Robinson, 1975;Jurgens et al, 1981;Grossberg and Kuperstein, 1986;Scudder, 1988;Dominey and Arbib, 1991;Moschovakis, 1994;Breznen and Gnadt, 1997) have been proposed about how it works. These models can be broadly classified into two basic types: position models in which the quantity to be canceled by feedback represents a position of the eye in the orbit (Robinson, 1975;Grossberg and Kuperstein, 1986), and vector models in which the quantity to be canceled is a motor error that can represent both the direction and length of a movement (Jurgens et al, 1981;Scudder, 1988;Moschovakis, 1994;Breznen and Gnadt, 1997).…”

“…One common assumption is the inclusion of a resetable integrator (RI) cell to provide a displacement feedback signal to cancel the motor error movement signal (Jurgens et al, 1981;Moschovakis, 1994). The activity profile of such a cell is typically a nearly linear increase in firing rate until the saccade ends, at which time the integrator is actively reset, thereby causing its activity to drop to zero.…”

Reversible inactivation of macaque frontal eye field

“…20), which repre- sents where the eye should go (Robinson 1975;van Gisbergen et al 1981;Jürgens et al 1981;Scudder 1988;van Gisbergen and van Opstal 1989;Waitzman et al 1991). E d needs to be a sustained signal: it not only represents where to go but also drives the saccade.…”

Neural dynamics of saccadic and smooth pursuit eye movement coordination during visual tracking of unpredictably moving targets

“…The vermis then monitors feedback information from brain stem about saccade velocity to steer and stop the saccade by inhibiting the FOR. This replaces the classical notion of a displacement integrator (Jurgens, Becker, & Kornhuber, 1981), which uses the desired change in eye position instead of the desired eye position as an input to the saccade generator. A major difference between the Optican and Quaia (2002) and Gancarz and Grossberg (1999) models lies in how the CBM corrects for saccadic errors.…”