Different stages of emotional prosody processing in healthy ageing-evidence from behavioural responses, ERPs, tDCS, and tRNS.

Past research suggests that the ability to recognise the emotional intent of a speaker decreases as a function of age. Yet, few studies have looked at the underlying cause for this effect in a systematic way. This paper builds on the view that emotional prosody perception is a multi-stage process and explores which step of the recognition processing line is impaired in healthy ageing using time-sensitive event-related brain potentials (ERPs). Results suggest that early processes linked to salience detection as reflected in the P200 component and initial build-up of emotional representation as linked to a subsequent negative ERP component are largely unaffected in healthy ageing. The two groups show, however, emotional prosody recognition differences: older participants recognise emotional intentions of speakers less well than younger participants do. These findings were followed up by two neuro-stimulation studies specifically targeting the inferior frontal cortex to test if recognition improves during active stimulation relative to sham. Overall, results suggests that neither tDCS nor high-frequency tRNS stimulation at 2mA for 30 minutes facilitates emotional prosody recognition rates in healthy older adults.

Perception of comfort during active and sham transcranial direct current stimulation: a double blind study.

BACKGROUND: A limited number of studies have assessed the tolerability and comfort experienced while undertaking transcranial direct current stimulation (tDCS). OBJECTIVE: This study intended to assess tolerability and the level of comfort experienced in a large sample of participants undertaking tDCS for 30 min at 2 mA of current strength. Moreover, we assessed whether sham and active stimulation are indistinguishable. METHODS: One-hundred and forty-nine participants underwent 195 tDCS sessions. The delivery of stimulation was double-blind. Participants were asked: (i) to rate comfort levels using a visual analog scale; (ii) to report any symptom experienced during the period of tDCS stimulation; (iii) to indicate, at the end of the session, whether the tDCS stimulation was active or sham. RESULTS: No adverse effects occurred. However, comfort levels were significantly higher in the sham than in the active stimulation condition (primarily in Study 2). A comparable number of symptoms were experienced in the active and in the sham conditions. However, in the majority of symptoms reported, a greater proportion of participants complained in the active than in the sham stimulation condition. Ancillary analyses indicated that with smaller electrodes more symptoms were experienced. However, this occurred in a comparable way in both active and sham stimulations. Finally, participants could not reliably distinguish the type of stimulation received. CONCLUSIONS: The present study adds and complements the growing literature suggesting that tDCS is a well-tolerated and safe neurostimulation tool. Moreover, at least under the stimulation parameters used in the present study, neurostimulation can be successfully administered using a double-blind procedure without participants being able to reliably assess whether the stimulation received is either active or sham.