The central mesencephalic reticular formation: its role in space-time coordinated saccadic eye movements

■ A small saccade of 0.5–3° that takes the eye away from fixation, followed by a saccade that returns the eye back to fixation after about 200 msec (i.e., presence of intersaccadic interval during which visual feedback occurs) ■ So named because of its appearance in eye movement tracings ■ Normal subjects often have square wave jerks (SWJ), but the rate is only 4–6 per minute. ■ Pathologic SWJ occurs at a rate of >15 per minute. ■ Cerebellar diseases Square wave jerks result from damage of projections from the frontal eye field, rostral pole of the superior colliculus, and the central mesencephalic reticular formation to the omnipause cells in the pons. If symptomatic, SWJ may be treated with methylphenidate, diazepam, phenobarbital, or amphetamines. ■ Burst of saccades with defective steps of innervation (i.e., stepless saccades) ■ Conjugate or monocular Saccadic pulses are associated with multiple sclerosis. Saccadic pulses result from damage of omnipause cells or the neural integrator.

Download Full-text

Response Properties of Saccade-Related Burst Neurons in the Central Mesencephalic Reticular Formation

Journal of Neurophysiology ◽

10.1152/jn.1997.78.4.2164 ◽

1997 ◽

Vol 78 (4) ◽

pp. 2164-2175 ◽

Cited By ~ 34

Author(s):

Ari Handel ◽

Paul W. Glimcher

Keyword(s):

Reticular Formation ◽

Light Emitting Diode ◽

Low Frequency ◽

Mesencephalic Reticular Formation ◽

Restricted Range ◽

Response Properties ◽

Burst Neurons ◽

Central Mesencephalic Reticular Formation ◽

Saccadic Target ◽

Behaving Monkeys

Handel, Ari and Paul W. Glimcher. Response properties of saccade-related burst neurons in the central mesencephalic reticular formation. J. Neurophysiol. 78: 2164–2175, 1997. We studied the activity of saccade-related burst neurons in the central mesencephalic reticular formation (cMRF) in awake behaving monkeys. In experiment 1, we examined the activity of single neurons while monkeys performed an average of 225 delayed saccade trials that evoked gaze shifts having horizontal and vertical amplitudes between 2 and 20°. All neurons studied generated high-frequency bursts of activity during some of these saccades. For each neuron, the duration and frequency of these bursts of activity reached maximal values when the monkey made movements within a restricted range of horizontal and vertical amplitudes. The onset of the movement followed the onset of the burst by the longest intervals for movements within a restricted range of horizontal and vertical amplitudes. The range of movements for which this interval was longest varied from neuron to neuron. Across the population, these ranges included nearly all contraversive saccades with horizontal and vertical amplitudes between 2 and 20°. In experiment 2, we used the following task to examine the low-frequency prelude of activity that cMRF neurons generate before bursting: the monkey was required to fixate a light-emitting diode (LED) while two eccentric visual stimuli were presented. After a delay, the color of the fixation LED was changed, identifying one of the two eccentric stimuli as the saccadic target. After a final unpredictable delay, the fixation LED was extinguished and the monkey was reinforced for redirecting gaze to the identified saccadic target. Some cMRF neurons fired at a low frequency during the interval after the fixation LED changed color but before it was extinguished. For many neurons, the firing rate during this interval was related to the metrics of the movement the monkey made at the end of the trial and, to a lesser degree, to the location of the eccentric stimulus to which a movement was not directed.

Download Full-text