The role of low-frequency rTMS in the superior parietal cortex during time estimation

Unpredictable fearful stimuli disrupt timing activities: Evidence from event-related potentials

The present study investigated the effect of an imminent fearful stimulus on an ongoing temporal task. Participants judged the duration of a blank temporal interval followed by a fearful or a neutral image. Results showed an underestimation of the duration in the fearful condition relative to the neutral condition, but only when the occurrence of the fearful image was difficult to predict. ERPs results for the blank temporal interval found no effect of the fearful stimulus on the contingent negative variation (CNV) amplitude in the clock stage. However, after the image onset, there was a larger P1 for the fearful relative to the neutral condition. Although this effect was indistinguishable regardless of whether the fearful event could be easily predicted, a late positive potential (LPP) component displayed larger amplitude only for unpredictable fearful stimuli. The time-frequency results showed enhanced delta-theta power (0.5-7.5 Hz) for the unpredictable fearful stimuli in the late stage. Importantly, the enhanced delta-theta rhythm correlated negatively with the duration judgments. Together, these results suggest that an unpredictable fearful event might divert more attention away from the counting process in the working memory stage, resulting in missing ticks and temporal underestimation.

Short-term neurophysiological effects of sensory pathway neurorehabilitation strategies on chronic poststroke oropharyngeal dysphagia

BACKGROUND

Neurorehabilitation strategies for chronic poststroke (PS) oropharyngeal dysphagia (OD) have been mainly focused on the neurostimulation of the pharyngeal motor cortex with only marginal effects. In contrast, treatments targeting the PS oropharyngeal sensory pathway dysfunction offer very promising results, but there is little knowledge on the underlying mechanisms. We aimed to explore the neurophysiological mechanisms behind the effect of three sensory neurostimulation strategies.

METHODS

We carried out a randomized two-blinded parallel group's crossover sham-controlled clinical trial in 36 patients with unilateral stroke and chronic unsafe swallow to investigate the effect of repetitive transcranial magnetic stimulation (rTMS) of the primary sensory cortex (A), oral capsaicin (B) and intra-pharyngeal electrical stimulation (IPES; C). The effect was evaluated immediately after the interventions with videofluoroscopy (VFS) and motor/sensory evoked potentials (MEP/SEP).

KEY RESULTS

Interventions induced no changes in the biomechanics of the swallow response during VFS. However, an enhancement of motor cortex excitability (latency shortening and increased size of thenar MEP) was found with active interventions (A + B + C, and B/C alone; P < .05 for all) but not with sham. Active but not sham interventions shortened pharyngeal SEP latency in the ipsilesional hemisphere (A + B + C: P2-peak, P = .039; A: N2-peak, P = .034) and antagonized the physiological habituation in pharyngeal MEP (A + B + C and A alone, P < .05 for both).

CONCLUSIONS AND INFERENCES

Sensory pathway neurostimulation strategies caused immediate enhancement of motor cortex excitability with peripheral strategies (capsaicin and IPES) and of pharyngeal sensory conduction with rTMS. These changes support the use of sensory neurorehabilitation strategies in promoting swallow recovery in chronic PS-OD.