2 research outputs found
Transcutaneous Electrical Nerve stimulation Effects on Neglect: A Visual-Evoked Potential Study
No full textWe studied the effects of transcutaneous electrical nerve stimulation (TENS) in six right-brain-damaged patients with left unilateral spatial neglect (USN), using both standard clinical tests (reading, line and letter cancellation, and line bisection), and electrophysiological measures (steady-state visual evoked potentials, SSVEP). TENS was applied on left neck muscles for 15’, and measures were recorded before, immediately after, and 60’ after stimulation. Behavioral results showed that the stimulation temporarily improved the deficit in all patients. In cancellation tasks, omissions and performance asymmetries between the two hand-sides were reduced, as well as the rightward deviation in line bisection. Before TENS, SSVEP average latency to stimuli displayed in the left visual half-field [LVF, (160 ms)] was remarkably longer than to stimuli shown in the right visual half-field [RVF, (120 ms)]. Immediately after TENS, latency to LVF stimuli was 130 ms; one hour after stimulation the effect of TENS faded, with latency returning to baseline. TENS similarly affected also the latency SSVEP of twelve healthy participants, and their line bisection performance, with effects smaller in size. The present study, first, replicates evidence concerning the positive behavioral effects of TENS on the manifestations of left USN in right-brain-damaged patients; second, it shows putatively related electrophysiological effects on the SSVEP latency. These behavioral and novel electrophysiological results are discussed in terms of specific directional effects of left somatosensory stimulation on egocentric coordinates, which in USN patients are displaced towards the side of the cerebral lesion. Showing that VEP latency is modulated by proprioceptive stimulation, we provide electrophysiological evidence to the effect that TENS may improve some manifestations of USN, with implications for its rehabilitation
The functional role of the medial motion area V6
No full textIn macaque, several visual areas are devoted to analyze motion in the visual field, and V6 is one of these areas. In macaque, area V6 occupies the ventral part of the anterior bank of the parieto-occipital sulcus (POS), is retinotopically-organized and contains a point-to-point representation of the retinal surface. V6 is a motion sensitive area that largely represents the peripheral part of the visual field and whose cells are very sensitive to translational motion. Based on the fact that macaque V6 contains many real-motion cells, it has been suggested that V6 is involved in object-motion recognition. Recently, area V6 has been recognized also in the human brain by neuroimaging and electrophysiological methods. Like macaque V6, human V6 is located in the POs, is retinotopically organized, and represents the entire contralateral hemifield up to the far periphery. Human V6, like macaque V6, is a motion area that responds to unidirectional motion. It has a strong preference for coherent motion and a recent combined VEPs/fMRI work has shown that area V6 is even one of the most early stations coding the motion coherence. Human V6 is highly sensitive to flow field and is also able to distinguish between different 3D flow fields being selective to translational egomotion. This suggests that this area processes visual egomotion signals to extract information about the relative distance of objects, likely in order to act on them, or to avoid them. The view that V6 is involved in the estimation of egomotion has been tested also in other recent fMRI studies. Thus, taken together, human and macaque data suggest that V6 is involved in both object and self-motion recognition. Specifically, V6 could be involved in 'subtracting out' self motion signals across the whole visual field and in providing information about moving objects, particularly during self-motion in a complex and dynamically unstable environment
