Faculty Bibliography

We studied ocular asymmetries and orienting responses induced by angular rotation in rabbits with binocular video recordings. Slow phase velocities were significantly larger in the eye moving temporonasally than nasotemporally. The eyes also converged and pitched down during rotation, which increased and refocused binocular overlap in the visual fields. Eye position also shifted into the slow phase direction. Vergence and pitch outlasted the induced nystagmus, suggesting that they were generated by a separate vestibulo-oculomotor subsystem(s). Thus, mechanisms in the rabbit increase compensatory eye velocity in the eye that leads into the direction of rotation and enhance binocular vision

Sinusoidal translation while rotating at constant angular velocity about a vertical axis (translation while rotating, TWR) produces centripetal and translational accelerations along the direction of translation and an orthogonal Coriolis acceleration due to the translation in the rotating frame. Thus, a Coriolis acceleration is produced along the bitemporal axis when oscillating along the naso-occipital axis, and along the naso-occipital axis when oscillating along the bitemporal axis. Together, these components generate an elliptically rotating acceleration vector that revolves around the head in the direction of rotation at the frequency of oscillation. Here we studied the orienting and compensatory responses of rabbits during TWR. Combinations of centripetal and translational accelerations were held constant at 0.5 g, and oscillation frequencies were varied from 0.01-0.33 Hz. The amplitude of the Coriolis acceleration increased with the frequency of translation. Naso-occipital translation caused vergence and pitch at all frequencies and roll at higher frequencies, and bitemporal translation produced roll at all frequencies and vergence and pitch at higher frequencies. The sensitivity of each ocular orienting component to linear acceleration was comparable across the different oscillation frequencies. TWR also induced continuous yaw nystagmus with slow phase velocity in the direction of rotation of the acceleration vector. Thresholds for appearance of nystagmus were 0.05 Hz, corresponding to a Coriolis acceleration of 0.06 g. Mean slow phase velocity for a rotating linear acceleration vector produced by 0.5 g along the translation axis and 0.34 g of Coriolis acceleration along the orthogonal axis were approximately 9 degrees /s. Eye velocities during TWR were similar to those generated by off-vertical axis rotation (OVAR), but were opposite in direction with regard to head rotation, following the direction of the rotating acceleration vector in both paradigms. Both are produced by activation of velocity storage in the vestibular system. One important difference between TWR and OVAR is that the head is always upright with regard to gravity during TWR. We speculate that the brain may use these low amplitude rotating linear accelerations to generate eye velocities that help to orient gaze when making turns during normal locomotion

We used the juxtacellular recording and labeling technique of Pinault (1996) in the uvula/nodulus of the ketamine anesthetized rat in an attempt to link different patterns of spontaneous activity with different types of morphologically identified cerebellar cortical interneurons. Cells displaying a somewhat irregular, syncopated cadence of spontaneous activity averaging 4-10 Hz could, upon successful entrainment and visualization, be morphologically identified as Golgi cells. Spontaneously firing cells with a highly or fairly regular firing rate of 10-35 Hz turned out to be unipolar brush cells. We also found indications that other types of cerebellar cortical neurons might also be distinguished on the basis of the characteristics of their spontaneous firing. Comparison of the interspike interval histograms of spontaneous activity obtained in the anaesthetized rat with those obtained in the awake rabbit points to a way whereby the behaviorally related modulation of specific types of interneurons can be studied. In particular, the spontaneous activity signatures of Golgi cells and unipolar brush cells anatomically identified in the uvula/nodulus of the anaesthetized rat are remarkably similar to the spontaneous activity patterns of some units we have recorded in the flocculus of the awake rabbit. The spontaneous activity patterns of at least some types of cerebellar interneurons clearly have the potential to serve as identifying signatures in behaving animals

Combat-related posttraumatic stress disorder (PTSD) is highly comorbid with other mental disorders. However, the nature of the relationship between PTSD and other mental disorders remains unclear. A discordant high-risk twin design was used on data from a sub-sample of the male-male twin pair members of the Vietnam Era Twin Registry to examine whether patterns of comorbidity are consistent with a psychopathological response to combat exposure or reflect familial vulnerability to psychopathology. Mental disorders were assessed via the Mental Health Diagnostic Interview Schedule Version I

Modulation of the complex spike activity of Purkinje cells in the cerebellar flocculus can convey not only visual signals but also nonvisual signals. The nonvisual complex spike modulation, which is readily observed with vestibular stimulation of the awake rabbit in darkness, is approximately in-phase with the concomitant simple spike modulation. This nonreciprocal relationship contrasts to the reciprocal relationship found when the rabbit is afforded vision

Orienting otolith-ocular reflexes were assessed in rabbits using static tilt, off-vertical axis rotation (OVAR) and sinusoidal oscillation about earth-horizontal axes. In all paradigms, head pitch produced ocular counter-pitch and vergence, and head roll produced ocular counter-roll and conjugate yaw version. Thus, vergence and version are essential components of orienting reflexes along the naso-occipital and bitemporal axes. Vergence and version caused misalignment between the axes of eye and head movement during pitch and roll head movements. Semicircular canal input broadened the band-pass of these orienting reflexes, which would make them more appropriate when compensating for head movement during active motion.

The caudal dorsal cap (dc) of the inferior olive is involved in the control of horizontal compensatory eye movements. It provides those climbing fibers to the vestibulocerebellum that modulate optimally to optokinetic stimulation about the vertical axis. This modulation is mediated at least in part via an excitatory input to the caudal dc from the pretectal nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system. In addition, the caudal dc receives a substantial GABAergic input from the nucleus prepositus hypoglossi (NPH). To investigate the possible contribution of this bilateral inhibitory projection to the visual responsiveness of caudal dc neurons, we recorded the climbing fiber activity (i.e., complex spikes) of vertical axis Purkinje cells in the flocculus of anesthetized rabbits before and after ablative lesions of the NPH. When the NPH ipsilateral to the recorded flocculus was lesioned, the spontaneous complex spike firing frequency did not change significantly; but when both NPHs were lesioned, the spontaneous complex spike firing frequency increased significantly. When only the contralateral NPH was lesioned, the spontaneous complex spike firing frequency decreased significantly. Neither unilateral nor bilateral lesions had a significant influence on the depth of complex spike modulation during constant velocity optokinetic stimulation or on the transient continuation of complex spike modulation that occurred when the constant velocity optokinetic stimulation stopped. The effects of the lesions on the spontaneous complex spike firing frequency could not be explained when only the projections from the NPH to the inferior olive were considered. Therefore we investigated at the electron microscopic level the nature of the commissural connection between the two NPHs. The terminals of this projection were found to be predominantly GABAergic and to terminate in part on GABAergic neurons. When this inhibitory commissural connection is taken into consideration, then the effects of NPH lesions on the spontaneous firing frequency of floccular complex spikes are qualitatively explicable in terms of relative weighting of the commissural and caudal dc projections of the NPH. In summary, we conclude that in the anesthetized rabbit the inhibitory projection of the NPH to the caudal dc influences the spontaneous firing frequency of floccular complex spikes but not their modulation by optokinetic stimulation