Kush Paul | PubMed Health

PubMed2006

Activity of omnipause neurons during "staircase saccades" elicited by persistent microstimulation of the superior colliculus.

We have recorded the activity of omnipause neurons (OPNs) in the raphe interpositus during so-called staircase saccades produced by prolonged activation of the superior colliculus (SC) by microstimulation. By showing that OPNs cyclically pause during the periodic movements produced by the steady activation function, we reveal the functional relationship of the OPNs within the recurrent brainstem network that produces dynamic, closed-loop, and feedback control of saccades. Despite persistent, steady activation of the SC, the OPNs followed the periodic activity of the brainstem burst generator. This reveals a dominant influence of the oscillating brainstem circuit over descending control from the SC.

Animals↗

PubMed2005

Irrepressible saccades from a tectal lesion in a Rhesus monkey.

We present a case of spontaneously occurring irrepressible saccades in an experimental Rhesus monkey. Though eye jerks are sometimes associated with cerebellar disease, central demyelination or brainstem lesions, there is little consensus on their neurological mechanisms. From neurological and anatomical investigation we report that these irrepressible saccades were caused by a discrete cerebrovascular accident that involved the rostral superior colliculus along with its commissure, and with minor invasion of periaqueductal gray and adjacent mesencephalic reticular formation. Other suspected structures, like the raphe interpositus, substantia nigra and the cerebellum, were unaffected.

Animals↗

PubMed2003

Reliable real-time spike discrimination during microstimulation.

A fundamental technical hurdle in systems neurophysiology has been to record the activity of individual neurons in situ while using microstimulation to activate inputs or outputs. Stimulation artifact at the recording electrode has largely limited the usefulness of combined stimulating and recording to using single stimulation pulses or to presenting brief trains of pulses to look for transient responses. We have developed an adaptive filter that in real time allows continuous extracellular isolation of individual neural spikes during sustained experimental microstimulation. Using signal detection analysis we now quantifiably demonstrate the reliability of spike recovery from stimulus-corrupted records. Recordings were made from the regular firing of action potentials from the oculomotor or trochlear nuclei of two macaque monkeys while stimulating at a variety of locations. We found that the adaptive filter technique gave a projected error rate of <1 in 10(4) and the detection index, d', was significantly better than two other methods tested: a 4-parameter 'window discriminator' technique and the sample-and-hold technique. This adaptive technique should generalize to any recording situation where a stereotyped, triggered transient might obscure a neural event and will significantly advance our knowledge in areas of electrophysiology where the experimental design requires prolonged microstimulation.

Action Potentials↗

PubMed2003

Modulation of calcium-activated potassium small conductance (SK) current in rat dopamine neurons of the ventral tegmental area.

Block of calcium-sensitive potassium SK current (gKCa([SK])) by apamin or bicuculline methiodide potentiates burst firing in dopamine neurons in the presence of N-methyl-D-aspartate (NMDA). The purpose of this study was to test the hypothesis that calcium entry through NMDA-gated channels can potentiate gKCa([SK]) in dopamine neurons in the ventral tegmental area. We used microelectrodes to record an outward tail current that was evoked by membrane depolarization under single-electrode voltage-clamp. Using bicuculline methiodide (50 microM) as a reversible inhibitor of gKCa([SK]), we found that NMDA (15 microM) reduced the peak amplitude of the outward tail current by 39%. Contrary to expectations, our results suggest that stimulation of NMDA receptors reduces the calcium-activated potassium gKCa([SK]), an effect that could facilitate NMDA-dependent burst firing.

Animals↗

PubMed2003

Spectral cancellation of microstimulation artifact for simultaneous neural recording in situ.

A fundamental technical hurdle in systems neurophysiology has been to record the activity of individual neurons in situ while using microstimulation to activate inputs or outputs. Stimulation artifact at the recording electrode has largely limited the usefulness of combined stimulating and recording to using single stimulation pulses (e.g., orthodromic and antidromic activation) or to presenting brief trains of pulses to look for transient responses (e.g., paired-pulse stimulation). Using an adaptive filter, we have developed an on-line method that allows continuous extracellular isolation of individual neuron spikes during sustained experimental microstimulation. We show that the technique accurately and robustly recovers neural spikes from stimulation-corrupted records. Moreover, we demonstrate that the method should generalize to any recording situation where a stereotyped, triggered transient might obscure a neural event.

Action Potentials↗