Transformation of spatiotemporal dynamics in the macaque vestibular system from otolith afferents to cortex.

Sensory signals undergo substantial recoding when neural activity is relayed from sensors through pre-thalamic and thalamic nuclei to cortex. To explore how temporal dynamics and directional tuning are sculpted in hierarchical vestibular circuits, we compared responses of macaque otolith afferents with neurons in the vestibular and cerebellar nuclei, as well as five cortical areas, to identical three-dimensional translational motion. We demonstrate a remarkable spatio-temporal transformation: otolith afferents carry spatially aligned cosine-tuned translational acceleration and jerk signals. In contrast, brainstem and cerebellar neurons exhibit non-linear, mixed selectivity for translational velocity, acceleration, jerk and position. Furthermore, these components often show dissimilar spatial tuning. Moderate further transformation of translation signals occurs in the cortex, such that similar spatio-temporal properties are found in multiple cortical areas. These results suggest that the first synapse represents a key processing element in vestibular pathways, robustly shaping how self-motion is represented in central vestibular circuits and cortical areas.

Long-term results of hang-back medial rectus recession.

PURPOSE: To report long-term results with the hang-back technique for medial rectus muscle recession. METHODS: Medical records of 341 consecutive patients who underwent unilateral or bilateral hang-back medial rectus recession were reviewed. The amount of recession was based on the size of the esotropia as measured at near fixation. Patients were divided into two groups according to age at onset of esotropia: patients <1 year comprised group 1 and patients > or = 1 year comprised group 2. Surgical outcomes were analyzed for all patients included in the study. RESULTS: A total of 189 patients met the inclusion criteria. In group 1 patients (n=32), average deviation improved from 48.3 prism diopters (PD) preoperatively to 1.1 PD postoperatively. Eleven patients required a second procedure: 9 with recurrent esotropia and 2 with consecutive exotropia. Average time to second procedure was 27.4 months. In group 2 patients (n=157), average deviation improved from 29.6 PD preoperatively to 1.1 PD postoperatively. Twenty-one patients required a second procedure: 20 with recurrent esotropia and 1 with consecutive exotropia. Average time to second procedure was 22.7 months. CONCLUSION: The hang-back technique represents a safe, effective alternative to conventional medial rectus recession.