Neuropsychologia
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Amnesia and linguistic deficits that are associated with thalamic damage have attracted the attention of researchers interested in identifying the neural networks involved in memory and language. The Papez circuit, which is composed of the hippocampus, mammillary body and anterior thalamic nuclei, was first proposed to be critical for memory. However, subsequently, the roles of the neural circuit consisting of the rhinal/parahippocampal cortices and the mediodorsal thalamic nuclei became evident. ⋯ The current study demonstrated that the mammillothalamic tract, which connects the mammillary body with the anterior thalamic nuclei, and the anterior and inferior thalamic peduncles, which contain neural fibers that extend from several thalamic nuclei to the anterior temporal, medial temporal and frontal cortices, are disrupted in anterior thalamic infarction. These extensive thalamo-cortical disconnections appear to be due to the dissection of the neural fibers that penetrate the ventral anterior nucleus of the thalamus. Our results suggest the following: (1) amnesia that is associated with anterior thalamic infarction is best interpreted in the context of dual/multiple-system theories of memory/amnesia that posit that multiple neural circuits connecting the anterior and mediodorsal thalamic nuclei with the hippocampus and rhinal/parahippocampal cortices work in concert to support memory function; and (2) the semantic deficits observed in this syndrome may be associated with thalamo-anterior temporal and thalamo-lateral frontal disconnections.
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The volar sides of the fingers can be seen as the haptic counterpart to the fovea for visual perception. This study assessed the localisation of individual tactile stimuli and spatiotemporal patterns presented to the volar side of the fingers. Participants performed the localisation task by pointing at the perceived positions with a 3D tracker. ⋯ Spatiotemporal integration along the fingers followed the predictions of the sensory saltation paradigm: The shorter the temporal delay between the two stimuli, the closer together they were perceived. For spatiotemporal patterns across fingers, the results were inconclusive: No general relationship between temporal delay and the difference between the perceived positions could be demonstrated, presumably because the effect could only be elicited in some finger combinations. Temporal delay did have, however, an effect on overall lateral shifts in localisation.
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We introduce an approach based on fast periodic oddball stimulation that provides objective, high signal-to-noise ratio (SNR), and behavior-free measures of the human brain's discriminative response to complex visual patterns. High-density electroencephalogram (EEG) was recorded for human observers presented with 60s sequences containing a base-face (A) sinusoidally contrast-modulated at a frequency of 5.88 Hz (F), with face size varying every cycle. Different oddball-faces (B, C, D...) were introduced at fixed intervals (every 4 stimuli = F/5 = 1.18 Hz: AAAABAAAACAAAAD...). ⋯ Face inversion or contrast-reversal did not affect the basic 5.88 Hz periodic response over medial occipital channels. However, these manipulations substantially reduced the 1.18 Hz oddball discrimination response over the right occipito-temporal region, indicating that this response reflects high-level processes that are partly face-specific. These observations indicate that fast periodic oddball stimulation can be used to rapidly and objectively characterize the discrimination of visual patterns and may become invaluable in characterizing this process in typical adult, developmental, and neuropsychological patient populations.
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Rightward prism adaptation has been shown to ameliorate visuospatial biases in right brain-damaged patients with neglect, and a single session of prism adaptation can lead to improvements that last up to several hours. Leftward prism adaptation in neurologically healthy individuals induces neglect-like biases in visuospatial tasks. The duration of these effects in healthy individuals, typically assumed to be ephemeral, has never been investigated. ⋯ These results demonstrate that both the sensorimotor and visuospatial effects last for at least 35 min, but that the visuospatial shift needs time to fully develop and fluctuates. By showing that the effects of prism adaptation in the undamaged brain are not ephemeral, these findings reveal the presence of another, so-far neglected dimension in the domain of the cognitive effects induced by prism adaptation, namely time. The prolonged duration of the induced visuospatial shift, previously considered to be a feature of prism adaptation unique to brain-damaged subjects, also applies to the normal brain.
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The mirror paradigm has been used extensively both as a research tool for studying kinesthesia in healthy individuals and as a therapeutic tool for improving recovery and/or alleviating symptoms in patients. The present study of healthy participants assessed the contribution of the mirror paradigm to motor control in a bimanual coordination task performed under sensorimotor disturbance conditions. In Experiment 1, the participants were required to produce symmetrical circles with both hands/arms at the same time. ⋯ However, motor performance in the mirror vision condition was little better than in the eyes closed condition, regardless of whether or not sensorimotor disturbance was applied. In Experiment 2, there were no differences between the "eyes closed" and "mirror vision" conditions. Although mirror reflection of one arm has been shown to induce consistent, vivid, perceptual illusions (kinesthetic illusion), our results suggest that it is less effective in modulating motor behavior.