CENTRAL CONTRtJL OF EVE MOVEMENTS 



1095 



FIG. 4. Location in the goat brain of 

 regions yielding microelectrode re- 

 sponses to afferent excitation from eye, 

 iaw and limb movement, and to visual 

 excitation. Sagittal section, 3 mm lateral 

 to mid-line, in the plane shown on the 

 diagram of the transverse section. 



hfy: 



Eye-musc!e responses 



• Latency short /// Nucleus and fibers of 



third nerve 

 3 Latency 20-50 IV Nucleus and fibers of 



msec fourth nerve 



® Latency 50-100 V Fibers of fifth nerve 



msec 

 © Latency 100-180 Vm Motor nucleus of 



msec 

 ® Repetitive 



O Inhibitory 



O No latency 

 available 



Jaw-muscle responses 

 A Latency short 

 A Latency long 



fifth nerve 

 17 Nucleus and fibers of 



si.\th nerve 

 I'll Nucleus and fibers of 



seventh nerve 

 Sup.Col. Superior collic- 



ulus 

 Iitf.Col. Inferior collic- 



ulus 



C.G. Central grey matter 

 S.C.P. Superior cerebel- 

 lar peduncle 



Visual responses 

 ♦ To focal stimu- 

 lation 



M.L.F. Medial longitu- 

 dinal fasciculus 

 O To general il- Teg.T. Tegmental tract 

 luminalion 



P-C. Posterior commissure 

 Limb responses -\- 



[From Cooper et al. (37).] 



spindles before the onset of vestibulo-ocular reflex 

 movement. The first sign of movement is a discharge 

 in the alpha motoneurons. Subsequently there is 

 usually a decrease in discharge of the afferent fibers 

 at the l^eginning of the tension increase in the muscle, 

 and this may or may not be followed by a later in- 

 crease in frequency of discharge (147). This point has 

 so far been examined only in vestibular reflex move- 

 ment, not in movement evoked from the colliculus 

 or the cortex. If a stretch reflex does not exist, dis- 

 charge in gamma motoneurons is unlikely to precede 

 discharge in alpha motoneurons. 



It has been suggested that the muscle spindles 

 may control tonic discharge in the smaller muscle 

 fibers of the outer surface. No difference in behavior 

 in tonic and phasic contraction between large and 

 small fibers has so far been observed, but further 

 observations should be made on monkeys. It still 

 remains possible that although the spindle does not 

 operate a length servomechanism as it seems to do in 

 skeletal muscle (62), it may play an important part 

 in adversive movements initiated from stimulation of 

 the retina (p. 1098). 



VESTIBUL.'kR REFLEXES 



These reflexes have been described by Magnus 

 (loi), Fischer (66) and Lorente de No (97). They 

 are usually divided into static and statokinetic re- 

 flexes, the latter being the responses produced by 

 movement, whether rotation or linear acceleration, 

 the former the maintained compensatory position 

 produced by alterations in posture. The static reac- 

 tions have been the object of much work in the past, 

 but the statokinetic reactions seem to be more im- 

 portant and more interesting. 



Reactions to Rotation in Horizontal Plane 



Rotation in a horizontal plane to the right causes 

 prompt contraction of the left lateral rectus muscle 

 and relaxation of the medial rectus in the rabbit (51) 

 and in the decerebrate cat. In man this reaction can 

 be seen if fixation is prevented while the subject is 

 rotated in a chair. Clearly the efifect of this reaction 

 is to reduce the movement of the visual axis while 

 the body and head move. In the rabbit the ampli- 



