1,721,191 research outputs found
Neural site of redundant target effect: electrophysiological evidence
No full textThe present study represents an attempt to find an electrophysiological correlate of the redundant targets effect, or RTE (i.e., the speeding up of reaction time, or RT, for redundant vs. single targets). Subjects made a speeded response either to one small checkerboard presented to the left or right of fixation or to a pair of identical checkerboards presented simultaneously to both hemifields. Both single and double targets could appear either in the upper or lower visual hemifield. The task required detection but not discrimination of the stimuli. During task performance, we recorded the event-related potentials (ERPs) elicited bp the checkerboard targets. As in previous studies, we found that manual RTs to bilatral stimuli were faster than those to unilateral stimuli. This effect was more marked for lower- than for upper-field stimuli and could not be ascribed to probability summation. In addition, we found that the P1 and N1 components of the visual ERP had a shorter latency for bilateral than for summed unilateral stimuli presented to the two hemifields. In parallel with the behavioral findings, the latency values for the above components showed a larger RTE for lower-field stimuli. These findings indicate that the RTE occurs at the level of early visual processing, probably in the extrastriate visual cortex, rather than at late decisional or premotor stages
The right inferior frontal cortex in response inhibition: A tDCS–ERP co-registration stud
No full textCross-modal properties of the primary somatosensory cortex: a by-product of Hebbian association learning
No full textBackground:
A growing body of evidence suggests the existence of a Tactile Mirror System in the human brain: the observation of tactile events activates the same cortical network implicated in tactile perception, including the primary somatosensory cortex (S1). It has been suggested that such crossmodal, mirror-like, responses of S1 may arise from Hebbian association learning plasticity: the contingency of seeing a touch and the feeling of a tactile sensation may reinforce synapses between visual and somatosensory neurons. We tested this hypothesis with a novel crossmodal Paired Associative Stimulation (PAS).
Methods:
In the crossmodal PAS, a visual stimulus depicting a hand being touched is repeatedly presented, paired with a Transcranical Magnetic Stimulation (TMS) pulse over S1. We investigated the efficacy of this protocol in inducing timing-dependent crossmodal plasticity, assessed in terms of changes of tactile acuity. Eighteen healthy participants took part in a within-subjects experiment: the inter-stimulus interval (ISI) between the seen touch and the TMS pulse varied across PAS sessions.
Results:
A significant improvement in tactile acuity was induced by the cross-modal PAS only at a selective (20 ms) ISI. The present result shows that associative plasticity within S1 can be effectively induced through vision, highlighting the existence of crossmodal plastic mechanisms
Modulation of brain activity by selective task sets observed using event-related potentials
No full textWe investigated the ability of subjects to shift dynamically between selective task sets, using informative trial-by-trial cues. Two tasks were used which involved non-overlapping neural systems and different hemispheric specialization. In a verbal task, subjects decided whether a letter string was a real word or a non-word. In a spatial task, subjects decided whether an angle was acute or obtuse. A behavioural experiment showed that performance improved when cues predicted the upcoming task (80% validity), compared to when neutral cues did not afford selective task sets. Event-related potentials (ERPs) revealed brain activity related to forming selective task expectations, to switching tasks, and to the modulation of target processing as a function of such expectations and switches. Activity predicting the probable task started over parietal electrodes 160 ms after cue presentation, while activity related to task switching started at frontal electrodes around 280 ms. Both types of activities developed before target onset. Target processing was significantly influenced by the validity of the cue prediction, including strong modulation of language-related potentials. These results show that it is possible to switch dynamically between task sets involving distinct neural systems, even before the appearance of an imperative target stimulus, and that the nature of the task sets can influence neural activity related to task-set reconfiguration. Selective task sets can in turn modulate the processing of target stimuli. The effects also apply to the case of foveally presented words, whose processing has often been hypothesized to be automatic and outside the influence of selective attention
Effects of right parietal transcranial magnetic stimulation on object identification and orientation judgments.
No full textModulation of cortical oscillatory activity during transcranial magnetic stimulation
No full textTranscranial magnetic stimulation (TMS) can transiently modulate cortical excitability, with a net effect depending on the stimulation frequency (/=5 Hz facilitation, at least for the motor cortex). This possibility has generated interest in experiments aiming to improve deficits in clinical settings, as well as deficits in the cognitive domain. The aim of the present study was to investigate the on-line effects of low frequency (1 Hz) TMS on the EEG oscillatory activity in the healthy human brain, focusing particularly on the outcome of these modulatory effects in relation to the duration of the TMS stimulation. To this end, we used the event-related desynchronization/synchronization (ERD/ERS) approach to determine the patterns of oscillatory activity during two consecutive trains of sham and real TMS. Each train of stimulation was delivered to the left primary motor cortex (MI) of healthy subjects over a period of 10 min, while EEG rhythms were simultaneously recorded. Results indicated that TMS induced an increase in the power of brain rhythms that was related to the period of the stimulation, i.e. the synchronization of the alpha band increased with the duration of the stimulation, and this increase was inversely correlated with motor-evoked potentials (MEPs) amplitude. In conclusion, low frequency TMS over primary motor cortex induces a synchronization of the background oscillatory activity on the stimulated region. This induced modulation in brain oscillations seems to increase coherently with the duration of stimulation, suggesting that TMS effects may involve short-term modification of the neural circuitry sustaining MEPs characteristics
Gli effetti di un Corso di Laurea Specialistica in Scienze Infermieristiche ed Ostetriche: studio esplorativo di follow-up a due anni.
No full textThe mismatch negativity as an index of cognitive decline for the early detection of Alzheimer’s disease
No full textOrienting of attention with eye and arrow cues and the effect of overtraining.
No full textIn contrast to the classical distinction between a controlled orienting of attention induced by central cues and an automatic capture induced by peripheral cues, recent studies suggest that central cues, such as eyes and arrows, may trigger a reflexive-like attentional shift. Yet, it is not clear if the attention shifts induced by these two cues are similar or if they differ in some important aspect. To answer this question, in Experiment 1 we directly compared eye and arrow cues in a counter-predictive paradigm while in Experiment 2 we compared the above cues with a different symbolic cue. Finally, in Experiment 3 we tested the role of over-learned associations in cueing effects. The results provide evidence that eyes and arrows induce identical behavioural effects. Moreover, they show that over-learned associations between spatially neutral symbols and the cued location play an important role in yielding early attentional effects
- …
