Highstein Stephen M.

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Stephen M.

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  • Article
    Golgi cells operate as state-specific temporal filters at the input stage of the cerebellar cortex
    (Society for Neuroscience, 2010-12-15) Heine, Shane A. ; Highstein, Stephen M. ; Blazquez, Pablo M.
    Cerebellar processing of incoming information begins at the synapse between mossy fibers and granule cells, a synapse that is strongly controlled through Golgi cell inhibition. Thus, Golgi cells are uniquely positioned to control the flow of information into the cerebellar cortex and understanding their responses during behavior is essential to understanding cerebellar function. Here we show, for the first time, that Golgi cells express a unique oculomotor-related signal that can be used to provide state- and time-specific filtering of granule cell activity. We used newly established criteria to identify the unique electrophysiological signature of Golgi cells and recorded these neurons in the squirrel monkey ventral paraflocculus during oculomotor behaviors. We found that they carry eye movement, but not vestibular or visual, information and that this eye movement information is only expressed within a specific range of eye positions for each neuron. In addition, simultaneous recordings of Golgi cells and nearby mossy fibers revealed that Golgi cells have the opposite directional tuning of the mossy fiber(s) that likely drive their responses, and that these responses are more sluggish than their mossy fiber counterparts. Because the mossy fiber inputs appear to convey the activity of burst–tonic neurons in the brainstem, Golgi cell responses reflect a time-filtered negative image of the motor command sent to the extraocular muscles. We suggest a role for Golgi cells in the construction of forward models of movement, commonly hypothesized as a major function of the cerebellar cortex in motor control.
  • Article
    Dynamic displacement of normal and detached semicircular canal cupula
    (Springer, 2009-06-10) Rabbitt, Richard D. ; Breneman, Kathryn D. ; King, Curtis ; Yamauchi, Angela M. ; Boyle, Richard ; Highstein, Stephen M.
    The dynamic displacement of the semicircular canal cupula and modulation of afferent nerve discharge were measured simultaneously in response to physiological stimuli in vivo. The adaptation time constant(s) of normal cupulae in response to step stimuli averaged 36 s, corresponding to a mechanical lower corner frequency for sinusoidal stimuli of 0.0044 Hz. For stimuli equivalent to 40–200 deg/s of angular head velocity, the displacement gain of the central region of the cupula averaged 53 nm per deg/s. Afferents adapted more rapidly than the cupula, demonstrating the presence of a relaxation process that contributes significantly to the neural representation of angular head motions by the discharge patterns of canal afferent neurons. We also investigated changes in time constants of the cupula and afferents following detachment of the cupula at its apex—mechanical detachment that occurs in response to excessive transcupular endolymph pressure. Detached cupulae exhibited sharply reduced adaptation time constants (300 ms–3 s, n = 3) and can be explained by endolymph flowing rapidly over the apex of the cupula. Partially detached cupulae reattached and normal afferent discharge patterns were recovered 5–7 h following detachment. This regeneration process may have relevance to the recovery of semicircular canal function following head trauma.