Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Adaptation of saccade gains in response to errors keeps vision and action co-registered in the absence of awareness or effort. Timing is key, as the visual error must be available shortly after the saccade is generated or adaptation does not occur. Here, we tested the hypothesis that when feedback is delayed, learning still occurs, but does so through small secondary corrective saccades. ⋯ We propose that saccade learning may be driven by different types of feedback teaching signals. One teaching signal relies upon a tight temporal relation with the saccade and contributes to obligatory learning independent of awareness. When this signal is ineffective due to delayed error feedback, a second compensatory teaching signal enables flexible adjustments to the spatial goal of saccades and helps maintain sensorimotor accuracy.
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Unilateral isometric muscle contractions increase motor-evoked potentials (MEPs) produced by transcranial magnetic stimulation not only in the contracting muscle but also in the resting contralateral homologous muscle. Corticospinal excitability in the M1 contralateral to the contracting muscle changes depending on the type of muscle contraction. Here, we investigated the possibility that corticospinal excitability in M1 ipsilateral to the contracting muscle is modulated in a contraction-type-dependent manner. ⋯ The results showed that MEPs in the contracting right FCR were the smallest during lengthening contraction. By contrast, MEPs in the resting left FCR were the largest during lengthening contraction, whereas the H-reflex was similar in the resting left FCR during the three types of muscle contraction. These results suggest that different types of unilateral muscle contraction asymmetrically modulate MEP size in the resting contralateral homologous muscle and in the contracting muscle and that this regulation occurs at the supraspinal level.
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Pain is a conscious experience, crucial for survival. To investigate the neural basis of pain perception in humans, a large number of investigators apply noxious stimuli to the body of volunteers while sampling brain activity using different functional neuroimaging techniques. These responses have been shown to originate from an extensive network of brain regions, which has been christened the Pain Matrix and is often considered to represent a unique cerebral signature for pain perception. ⋯ Because the interpretation of a great number of experimental studies relies on the assumption that the brain responses elicited by nociceptive stimuli reflect the activity of a cortical network that is at least partially specific for pain, it appears crucial to ascertain whether this notion is supported by unequivocal experimental evidence. Here, we will review the original concept of the "Neuromatrix" as it was initially proposed by Melzack and its subsequent transformation into a pain-specific matrix. Through a critical discussion of the evidence in favor and against this concept of pain specificity, we show that the fraction of the neuronal activity measured using currently available macroscopic functional neuroimaging techniques (e.g., EEG, MEG, fMRI, PET) in response to transient nociceptive stimulation is likely to be largely unspecific for nociception.
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The aim of this study was to examine corticomotor excitability and plasticity following repetitive thumb abduction training in left and right hands of young and old adults. Electromyographic recordings were obtained from the abductor pollicis brevis (APB) muscle of 12 young (aged 18-27 years) and 14 old (aged 63-75 years) adults. Motor training consisted of 300 ballistic abductions of the thumb to maximize peak abduction acceleration, with each hand tested in a separate session. ⋯ Furthermore, no difference in use-dependent plasticity was observed between young and old adults, and SICI remained unchanged following ballistic training for both hands in all subjects. These findings suggest that there is greater strengthening of corticomotor circuits for control of the left compared with the right hand during simple ballistic thumb training and that an age-related decline in motor learning was observed only in the dominant hand. In contrast to previous studies, these data also indicate that young and old adults can demonstrate similar use-dependent corticomotor plasticity during this simple thumb-training task.
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Dense array event-related potentials (ERPs) and memory performance were assessed following rapid serial visual presentation (RSVP) of emotional and neutral pictures. Despite the extremely brief presentation, emotionally arousing pictures prompted an enhanced negative voltage over occipital sensors, compared to neutral pictures, replicating previous encoding effects. ⋯ ERPs measured during the recognition test showed both an early (250-350 ms) frontally distributed difference between hits and correct rejections, and a later (400-500 ms), more centrally distributed difference, consistent with effects of recognition on ERPs typically found using slower presentation rates. The data are consistent with the hypothesis that features of affective pictures pop out during rapid serial visual presentation, prompting better memory performance.