Journal of neurophysiology
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Comparative Study
Crossmodal integration in the primate superior colliculus underlying the preparation and initiation of saccadic eye movements.
Saccades to combined audiovisual stimuli often have reduced saccadic reaction times (SRTs) compared with those to unimodal stimuli. Neurons in the intermediate/deep layers of the superior colliculus (dSC) are capable of integrating converging sensory inputs to influence the time to saccade initiation. To identify how neural processing in the dSC contributes to reducing SRTs to audiovisual stimuli, we recorded activity from dSC neurons while monkeys generated saccades to visual or audiovisual stimuli. ⋯ Instead, the reduction in SRT for high-intensity, aligned audiovisual stimuli was correlated with increased premotor activity (activity after visual burst but preceding saccade-aligned burst). These data provide a link between changes in neural activity related to stimulus modality with changes in behavior. They further demonstrate how crossmodal interactions are not limited to the initial sensory activity but can also influence premotor activity in the SC.
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Editorial Historical Article
The physiology of the peripheral vestibular system: the birth of a field.
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Comparative Study
Cortical and subcortical correlates of electroencephalographic alpha rhythm modulation.
Neural correlates of electroencephalographic (EEG) alpha rhythm are poorly understood. Here, we related EEG alpha rhythm in awake humans to blood-oxygen-level-dependent (BOLD) signal change determined by functional magnetic resonance imaging (fMRI). Topographical EEG was recorded simultaneously with fMRI during an open versus closed eyes and an auditory stimulation versus silence condition. ⋯ The inverse relationship between EEG alpha amplitude and BOLD signals in primary and secondary visual areas suggests that widespread thalamocortical synchronization is associated with decreased brain metabolism. While the temporal relationship of this association is consistent with metabolic changes occurring simultaneously with changes in the alpha rhythm, sites in the medial thalamus and in the anterior midbrain were found to correlate with short time lag. Assuming a canonical hemodynamic response function, this finding is indicative of activity preceding the actual EEG change by some seconds.
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Comparative Study
Temporomandibular joint inflammation potentiates the excitability of trigeminal root ganglion neurons innervating the facial skin in rats.
The aim of this study was to test the hypothesis that temporomandibular joint (TMJ) inflammation alters the excitability of trigeminal root ganglion (TRG) neurons innervating the facial skin, by using behavioral, electrophysiological, molecular, and immunohistochemical approaches. Complete Freund's adjuvant (CFA) was injected into the rat TMJ to produce inflammation. The threshold for escape from mechanical stimulation applied to the orofacial area in TMJ-inflamed rats was significantly lower than that in naïve rats. ⋯ Quantitative single-cell RT-PCR analysis showed the increased expression of mRNA for the NK1 receptor in FG-labeled TRG neurons in inflamed rats compared with that in naive rats. The numbers of SP and NK1 receptors/neurofilament 200 positive immunoreactive TRG neurons innervating the facial skin (FG-labeled) in the inflamed rats were significantly increased compared with those seen in naïve rats. These results suggest that TMJ inflammation can alter the excitability of medium- and large-diameter TRG neurons innervating the facial skin and that an increase in SP/NK1 receptors in their soma may contribute to the mechanism underlying the trigeminal inflammatory allodynia in the TMJ disorder.
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Comparative Study
Fimbria-fornix lesions compromise the induction of long-term potentiation at the Schaffer collateral-CA1 synapse in the rat in vivo.
Although bilateral fimbria-fornix (FF) lesioning impairs spatial performance in animals, the literature is equivocal regarding its effects on hippocampal long-term potentiation (LTP). We examined the effects of FF lesioning on LTP induction in the Schaffer collateral-CA1 pathway in vivo with a protocol that delivered theta burst stimulation (TBS) trains of increasing length until a sufficient length was reached to induce LTP of the monosynaptic field excitatory postsynaptic potential (fEPSP). Experiments were performed in urethan-anesthetized Long-Evans rats either 4 or 12-16 wk after lesioning. ⋯ In contrast, animals in the 12- to 16-wk post-lesion group showed a highly significant deficit in LTP induction (95 +/- 3% of control fEPSP slope; n = 8; < or =28 burst TBS trains tested; P < 0.001 vs. sham- and 4-wk post-FF-lesion groups). Other quantitative measures of synaptic excitability (i.e., baseline fEPSP slope and input-output relation) did not differ between the sham- and the 12- to 16-wk post-FF-lesion groups. These results indicate that the FF lesion leads to an enduring defect in hippocampal long-term synaptic plasticity that may relate mechanistically to the cognitive deficits characterized in this model.