. The interstitial nucleus of Cajal (INC) is thought to be the "neural integrator" for torsional/vertical eye position and head posture. Here, we investigated the coordination of eye and head movements after reversible INC inactivation. Three-dimensional (3-D) eye-head movements were recorded in three head-unrestrained monkeys using search coils. INC sites were identified by unit recording/electrical stimulation and then reversibly inactivated by 0.3 l of 0.05% muscimol injection into 26 INC sites. After muscimol injection, the eye and head 1) began to drift (an inability to maintain stable fixation) torsionally: clockwise (CW)/ counterclockwise (CCW) after left/right INC inactivation respectively.2) The eye and head tilted torsionally CW/CCW after left/right INC inactivation, respectively. Horizontal gaze/head drifts were inconsistently present and did not result in considerable position offsets. Vertical eye drift was dependent on both vertical eye position and the magnitude of the previous vertical saccade, as in head-fixed condition. This correlation was smaller for gaze and head drift, suggesting that the gaze and head deficits could not be explained by a first-order integrator model. Ocular counterroll (OC) was completely disrupted. The gain of torsional vestibuloocular reflex (VOR) during spontaneous eye and head movements was reduced by 22% in both CW/CCW directions after either left or right INC inactivation. Our results suggest a complex interdependence of eye and head deficits after INC inactivation during fixation, gaze shifts, and VOR. Some of our results resemble the symptoms of spasmodic torticollis (ST).

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The India‐Asia collision resulted in the Cenozoic framework of faults, ranges, and tectonic basins and the high topography of the northeastern Tibetan Plateau, but how and when these features formed remains poorly understood, leading to conflicting tectonic models. However, information on the tectonic evolution of these active orogenic belts is well preserved in synorogenic basin sediments. In this study, we carefully analyze the detrital apatite fission track ages of Cenozoic synorogenic sediments from the Jiuquan Basin to decipher the entire exhumation process of the adjacent Qilian Shan throughout the Cenozoic. Our data indicate that initially rapid Cenozoic exhumation occurred in the Qilian Shan during the late Paleocene‐early Eocene (~60–50 Ma), almost synchronous with the India‐Asia collision. The Qilian Shan subsequently experienced long‐lived exhumation that continued until at least the middle Miocene (~45–10 Ma). During this period of exhumation in the Qilian Shan, tectonic deformation occurred throughout the northeastern Tibetan Plateau. The early Cenozoic deformation in the northeastern Tibetan Plateau may have been caused by the transfer of tectonic stress from the distant India‐Asia collision boundary through the complex lithospheric environment of the Tibetan Plateau. The present tectonic configuration and topography of the Qilian Shan and the northeastern Tibetan Plateau likely became established since the middle Miocene and after the long‐lived deformation began in the early Cenozoic.

The interstitial nucleus of Cajal (INC) is thought to control torsional and vertical head posture. Unilateral microstimulation of the INC evokes torsional head rotation to positions that are maintained until stimulation offset. Unilateral INC inactivation evokes head position-holding deficits with the head tilted in the opposite direction. However, the underlying muscle synergies for these opposite behavioral effects are unknown. Here, we examined neck muscle activity in head-unrestrained monkeys before and during stimulation (50 muA, 200 ms, 300 Hz) and inactivation (injection of 0.3 mul of 0.05% muscimol) of the same INC sites. Three-dimensional eye and head movements were recorded simultaneously with electromyographic (EMG) activity in six bilateral neck muscles: sternocleidomastoid (SCM), splenius capitis (SP), rectus capitis posterior major (RCPmaj.), occipital capitis inferior (OCI), complexus (COM), and biventer cervicis (BC). INC stimulation evoked a phasic, short-latency ( approximately 5-10 ms) facilitation and later ( approximately 100-200 ms) a more tonic facilitation in the activity of ipsi-SCM, ipsi-SP, ipsi-COM, ipsi-BC, contra-RCPmaj., and contra-OCI. Unilateral INC inactivation led to an increase in the activity of contra-SCM, ipsi-SP, ipsi-RCPmaj., and ipsi-OCI and a decrease in the activity of contra-RCPmaj. and contra-OCI. Thus the influence of INC stimulation and inactivation were opposite on some muscles (i.e., contra-OCI and contra-RCPmaj.), but the comparative influences on other neck muscles were more variable. These results show that the relationship between the neck muscle responses during INC stimulation and inactivation is much more complex than the relationship between the overt behaviors.

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