Alberto Pisoni

Separating Recognition Processes of Declarative Memory via Anodal tDCS: Boosting Old Item Recognition by Temporal and New Item Detection by Parietal Stimulation

There is emerging evidence from imaging studies that parietal and temporal cortices act together to achieve successful recognition of declarative information; nevertheless, the precise role of these regions remains elusive. To evaluate the role of these brain areas in declarative memory retrieval, we applied bilateral tDCS, with anode over the left and cathode over the right parietal or temporal cortices separately, during the recognition phase of a verbal learning paradigm using a balanced old-new decision task. In a parallel group design, we tested three different groups of healthy adults, matched for demographic and neurocognitive status: two groups received bilateral active stimulation of either the parietal or the temporal cortex, while a third group received sham stimulation. Accuracy, discriminability index (d’) and reaction times of recognition memory performance were measurements of interest. The d’ sensitivity index and accuracy percentage improved in both active stimulation groups, as compared with the sham one, while reaction times remained unaffected. Moreover, the analysis of accuracy revealed a different effect of tDCS for old and new item recognition. While the temporal group showed enhanced performance for old item recognition, the parietal group was better at correctly recognising new ones. Our results support an active role of both of these areas in memory retrieval, possibly underpinning different stages of the recognition process.

Specific disgust processing in the left insula: New evidence from direct electrical stimulation

Neuropsychological and neuroimaging studies yielded controversial results concerning the specific role of the insula in recognizing the facial expression of disgust. To verify whether the insula has a selective role in facial disgust processing, emotion recognition was studied in thirteen patients during intraoperative stimulation of the insula in awake surgery performed for removal of a glioma close to this structure. Direct electrical stimulation of the left insula produced a general decrease in emotion recognition but only in the case of disgust there was a statistically significant detrimental effect (p=0.004). Happiness and anger were the best and the worst recognized emotion, respectively. The worst baseline performance with anger and, partly, fear could be explained with the involvement of the left temporal regions, striatum, and the connection between the striatum and the frontal lobe, as suggested in previous studies. Therefore, upon these intra-operative evidences, we argue for a selective role of the left insula in disgust recognition, although a (non significant) decrease in the recognition of other negative emotions was found. However, additional networks can develop, as demonstrated by the fact that disgust recognition was not impaired after surgery even in patients with insular resection in the current as in previous studies.

Cognitive Enhancement Induced by Anodal tDCS Drives Circuit-Specific Cortical Plasticity

Increasing evidence shows that anodal transcranial direct current stimulation (tDCS) enhances cognitive performance in healthy and clinical population. Such facilitation is supposed to be linked to plastic changes at relevant cortical sites. However, direct electrophysiological evidence for this causal relationship is still missing. Here, we show that cognitive enhancement occurring in healthy human subjects during anodal tDCS is affected by ongoing brain activity, increasing cortical excitability of task-related brain networks only, as directly measured by Transcranial Magnetic Stimulation combined with electroencephalography (TMS-EEG). Specifically, TMS-EEG recordings were performed before and after anodal tDCS coupled with a verbal fluency task. To control for effects of tDCS protocol and TMS target location, 3 conditions were assessed: anodal/sham tDCS with TMS over left premotor cortex, anodal tDCS with TMS over left posterior parietal cortex. Modulation of cortical excitability occurred only at left Brodmanns areas 6, 44, and 45, a key network for language production, after anodal tDCS and TMS over the premotor cortex, and was positively correlated to the degree of cognitive enhancement. Our results suggest that anodal tDCS specifically affects task-related functional networks active while delivering stimulation, and this boost of specific cortical circuits is correlated to the observed cognitive enhancement.

Safety of 5 kHz tACS

BACKGROUND Sinusoidal transcranial alternating current stimulation (tACS) at 5 kHz applied for 10 min at 1 mA intensity over the hand area of the primary motor cortex (M1) results in sustained changes in cortical excitability as previously demonstrated. OBJECTIVE Here we have assessed safety aspects of this stimulation method by measuring neuron-specific enolase (NSE) levels, examining electroencephalogram (EEG) traces and analyzing anatomical data by using magnetic resonance imaging (MRI). METHODS Altogether 18 healthy volunteers participated in the study. tACS was applied at 5 kHz for a duration of 10 min over the left M1 at an intensity of 1 mA. RESULTS After stimulation no significant changes were detected in NSE levels, no structural alterations were observed in the anatomical scans and no pathological changes were found in the EEG recordings. CONCLUSIONS Our data imply that the application of tACS is safe at least within these parameters and with these applied protocols.

Bi-frontal transcranial alternating current stimulation in the ripple range reduced overnight forgetting

High frequency oscillations in the hippocampal structures recorded during sleep have been proved to be essential for long-term episodic memory consolidation in both animals and in humans. The aim of this study was to test if transcranial Alternating Current Stimulation (tACS) of the dorsolateral prefrontal cortex (DLPFC) in the hippocampal ripple range, applied bi-frontally during encoding, could modulate declarative memory performance, measured immediately after encoding, and after a nights sleep. An associative word-pair learning test was used. During an evening encoding phase, participants received 1 mA 140 Hz tACS or sham stimulation over both DLPFCs for 10 min while being presented twice with a list of word-pairs. Cued recall performance was investigated 10 min after training and the morning following the training session. Forgetting from evening to morning was observed in the sham condition, but not in the 140 Hz stimulation condition. 140 Hz tACS during encoding may have an effect on the consolidation of declarative material.

TDCS effects on verbal fluency: A response to Vannorsdall et al (2016)

In a prior study (Cattaneo et al, 2011. Neuroscience. 183:64-70), we demonstrated that anodal transcranial direct current stimulation (tDCS) over the left inferior frontal gyrus enhanced verbal fluency in healthy young adults. Although our data are in line with the results of other published studies, another research group recently failed to report anodal tDCS effects on verbal fluency using a paradigm similar to ours (Vannorsdall et al, 2016. Cogn Behav Neurol. 29:11-17). Here we discuss aspects of study design and interpretation of results that should be considered in replications, focusing particularly on homogeneity of procedures. Notwithstanding the possibility that our study may indeed not be replicable, we hypothesize that Vannorsdall et al found an interesting modifier of the tDCS effects on verbal production by introducing a critical methodologic difference from our original study. We demonstrate this difference by presenting the results of an additional experiment. We believe that the sharing of data between research groups and constructive debate on possible differences in results should be encouraged because they help define the boundaries of applicability of an experimental paradigm. This is even more important for research findings that may have clinical implications, as is the case here.

Modulation of negative emotions through anodal tDCS over the right ventrolateral prefrontal cortex

ABSTRACT Increasing evidence suggests that the right ventrolateral prefrontal cortex (rVLPFC) plays a critical role in emotion regulation, in particular concerning negative feelings. In the present research, we applied anodal transcranial direct current stimulation (tDCS) over the rVLPFC with a twofold purpose. First, we aimed at exploring the feasibility of modulating the subjective experience of emotions through tDCS in healthy participants. Second, we wanted to assess which specific emotion can be regulated (and which cannot) with this brain stimulation approach. We designed a double‐blind, between‐subjects, sham‐controlled study in which 96 participants watched short video clips eliciting different emotions during anodal or sham tDCS over the rVLPFC. Emotional reactions to each video clip were assessed with self‐report scales measuring eight basic emotions. Results showed that, in contrast to the sham condition, tDCS over the rVLPFC reduced the perceived extent of specific negative emotions, namely, fear, anxiety, and sadness, compared to other negative or positive feelings. Overall, these results support the role of rVLPFC in regulating negative emotions, mostly associated with the prevention of dangerous situations (i.e., fear, anxiety, and sadness). HighlightsAnodal tDCS over rVLPFC modulated negative emotion perception.TDCS specifically reduced anxiety and fear induced by video clips.rVLPFC is involved in the regulation of certain negative emotions.Anodal tDCS can be effectively used to boost emotion regulation.

Contents Vol. 49, 2016

Founded 1897 as ‘Monatsschrift für Psychiatrie und Neurologie’, continued 1957–1967 as ‘Psychiatria et Neurologia’, continued 1968–1983 as ‘Psychiatria Clinica’ Founders: C. Wernicke and Th. Ziehen Successors: K. Bonhoeffer (1912–1938), J. Klaesi (1939–1967), E. Grünthal (1953–1973), N. Petrilowitsch (1968–1970), Th. Spoerri (1971–1973), P. Berner (1974–1999), E. Gabriel (1974–2004), Ch. Mundt (2000–2011)