Dana Cohen

Invariant phase structure of olivo-cerebellar oscillations and its putative role in temporal pattern generation.

Complex movements require accurate temporal coordination between their components. The temporal acuity of such coordination has been attributed to an internal clock signal provided by inferior olivary oscillations. However, a clock signal can produce only time intervals that are multiples of the cycle duration. Because olivary oscillations are in the range of 5–10 Hz, they can support intervals of ≈100–200 ms, significantly longer than intervals suggested by behavioral studies. Here, we provide evidence that by generating nonzero-phase differences, olivary oscillations can support intervals shorter than the cycle period. Chronically implanted multielectrode arrays were used to monitor the activity of the cerebellar cortex in freely moving rats. Harmaline was administered to accentuate the oscillatory properties of the inferior olive. Olivary-induced oscillations were observed on most electrodes with a similar frequency. Most importantly, oscillations in different recording sites retained a constant phase difference that assumed a variety of values in the range of 0–180°, and were maintained across large global changes in the oscillation frequency. The inferior olive may thus underlie not only rhythmic activity and synchronization, but also temporal patterns that require intervals shorter than the cycle duration. The maintenance of phase differences across frequency changes enables the olivo-cerebellar system to replay temporal patterns at different rates without distortion, allowing the execution of tasks at different speeds.

The functional architecture of the shark's dorsal-octavolateral nucleus: an in vitro study.

SUMMARY Learning to predict the component in the sensory information resulting from the organisms own activity enables it to respond appropriately to unexpected stimuli. For example, the elasmobranch dorsal octavolateral nucleus (DON) can apparently extract the unexpected component (i.e. generated by nearby organisms) from the incoming electrosensory signals. Here we introduce a novel and unique experimental approach that combines the advantages of in vitro preparations with the integrity of in vivo conditions. In such an experimental system one can study, under control conditions, the cellular and network mechanisms that underlie cancellation of expected sensory inputs. Using extracellular and intracellular recordings we compared the dynamics and spatiotemporal organization of the electrosensory afferent nerve and parallel fiber inputs to the DON. The afferent nerve has a low threshold and high conduction velocity; a stimulus that recruits a small number of fibers is sufficient to activate the principal neurons. The excitatory postsynaptic potential in the principal cells evoked by afferent nerve fibers has fast kinetics that efficiently reach the threshold for action potential. In contrast, the parallel fibers have low conduction velocity, high threshold and extensive convergence on the principal neurons of the DON. The excitatory postsynaptic response has slow kinetics that provides a wide time window for integration of inputs. The highly efficient connection between the afferent nerve and the principal neurons in the DON indicates that filtration occurring in the DON cannot be mediated simply by summation of the parallel fibers signals with the afferent sensory signals. Hence we propose that the filtering may be mediated via secondary neurons that adjust the principal neurons sensitivity to afferent inputs.

Towards a unified account of intensive reflexives

This paper examines intensive reflexives in an attempt to provide a unified account for the distributional properties they display, while rejecting an account in terms of polysemy. The proposed analysis provides a discourse notion of comparison which accounts for their distribution and the range of their interpretations.

Optical Insights Into Cerebellar Circuitry

It is commonly accepted that a deeper understanding of how neural networks function will depend on the ability to monitor brain activity with high temporal and spatial resolution. The need for such monitoring systems led in the early seventies to the development of optical imaging techniques using voltage-sensitive dyes (Ross et al. 1974). The technique is based on the detection of light emitted from special dye molecules that bind to membranes and fluoresce proportionally to the membrane potential. In its current state the method is particularly suitable for monitoring synchronized activity in large neuron populations as demonstrated here in the cerebellar cortex.

A model of how rapid changes in local input resistance of shark electrosensory neurons may enable detection of small signals

Sharks and other elasmobranchs hunt by detecting weak electric fields produced by their prey (Kalmijn, 1982). The behavioural threshold for initiating an electrically-guided attack is a few nanovolts (Kalmijn, 1982), but the sensitivity of primary afferent neurons is in the order of a few spikes per second per microvolt (Montgomery, 1984a; Conley and Bodznick, 1994). Thus the change in afferent firing rate caused by prey at the threshold is in the order of 1 spike per minute, or about 0.1% of the spontaneous rate (~15/sec, Montgomery, 1984a).