Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Previous studies have looked at co-processing of multiple proprioceptive inputs but few have investigated the effect of separate dynamic and tonic predominantly proprioceptive disruptions applied concurrently at the same segment. The purpose of the present study was to investigate how simultaneous ankle tendon vibration, a tonic stimulus, with a dynamic toes-up (TU) or toes-down (TD) platform perturbation (1) affects postural stability and (2) influences the adaptation process. Sixteen normal subjects (ten male, six female, mean age 26 +/- 4.8 years) stood blindfolded on a moving platform with vibrators attached bilaterally over the Achilles tendons. ⋯ In conclusion, although vibration significantly affects postural measures when applied in isolation, this finding does not hold when it is applied in combination with a more dynamic stimulus. Instead it seems that once postural stability has been disrupted the central nervous system can rapidly assess information from a weaker tonic input and utilise or suppress it appropriately, depending on its effect towards overall postural control. It can be concluded that postural responses to the concurrent application of different predominantly proprioceptive stimuli are dependent upon the type of stimulus and the ability of the central nervous system to rapidly assess and re-weigh available sensory inputs.
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Medial olivocochlear (MOC) neurons project to outer hair cells (OHC), forming the efferent arm of a reflex that affects sound processing and offers protection from acoustic overstimulation. The central pathways that trigger the MOC reflex in response to sound are poorly understood. Insight into these pathways can be obtained by examining the responses of single MOC neurons recorded from anesthetized guinea pigs. ⋯ The MOC reflex interneurons are thus likely to be chopper units of PVCN. Also supporting this conclusion, chopper units and MOC neurons both have sharp frequency tuning. Thus, the most likely pathway for the sound-evoked MOC reflex begins with the responses of hair cells, proceeds with type I auditory-nerve fibers, PVCN chopper units, and MOC neurons, and ends with the MOC terminations on OHC.
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Fos-like immunoreactivity (FLI) was evaluated in auditory and nonauditory brain structures in hamsters that had been exposed previously to intense sound and tested behaviorally for tinnitus. The immunocytochemical results demonstrated a significant increase in exposed animals of FLI in auditory brain structures such as the lateral lemniscus, central nucleus of inferior colliculus, and auditory cortex, as well as in some nonauditory brain structures such as the locus coeruleus, lateral parabrachial nucleus, certain subregions of the hypothalamus, and amygdala. ⋯ This is consistent with the hypothesis that FLI induced by intense sound exposure might represent a neural correlate of tinnitus or of plasticity associated with tinnitus. The possibility and the mechanisms underlying the increased FLI are discussed.
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Transcranial magnetic stimulation (TMS) has been used to assess characteristics of the corticomotor control of the jaw muscles, but less is known about the cortical control of the human tongue and its modification by training. The aim of the present study was to determine the effect of training humans in a novel tongue-protrusion task for 1 week on corticomotor excitability as assessed by changes in electromyographic activity elicited in the tongue musculature by TMS, and in the tongue cortical motor map revealed by TMS. Eleven healthy subjects participated. ⋯ No significant effect of the training on MEPs in the FDI was observed (P = 0.493). Analysis of the corticomotor topographic maps revealed a significant ( P<0.05) increase in excitability and, hence, the cortical area from which TMS could evoke MEPs in the tongue, although the center of gravity representation for the tongue or FDI muscles remained stable. The present findings suggest that a specific and reversible plasticity of the corticomotor excitability related to tongue muscle control can be induced when humans learn to perform successfully a novel tongue task.
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Background. The brain-gut interaction is important for the understanding of pain mechanisms related to gastroenterological diseases. Unfortunately little is known about the early cerebral events related to the processing of gut-evoked pain. ⋯ Conclusion. Short latency (50-60 ms) EPs to painful electrical sigmoid colon stimulation were demonstrated, reflecting an early cortical processing of sensory input from the sigmoid colon. The early cortical processing of somatic input from experimentally evoked visceral referred pain areas did not cause any detectable short-term cortical reorganization.