Stimulation Of Left Prefrontal Cortex Research Articles

Local Prefrontal Cortex TMS-Induced Reactivity Is Related to Working Memory and Reasoning in Middle-Aged Adults.

IntroductionThe prefrontal cortex (PFC) plays a crucial role in cognition, particularly in executive functions. Cortical reactivity measured with Transcranial Magnetic Stimulation combined with Electroencephalography (TMS-EEG) is altered in pathological conditions, and it may also be a marker of cognitive status in middle-aged adults. In this study, we investigated the associations between cognitive measures and TMS evoked EEG reactivity and explored whether the effects of this relationship were related to neurofilament light chain levels (NfL), a marker of neuroaxonal damage.MethodsFifty two healthy middle-aged adults (41–65 years) from the Barcelona Brain Health Initiative cohort underwent TMS-EEG, a comprehensive neuropsychological assessment, and a blood test for NfL levels. Global and Local Mean-Field Power (GMFP/LMFP), two measures of cortical reactivity, were quantified after left prefrontal cortex (L-PFC) stimulation, and cognition was set as the outcome of the regression analysis. The left inferior parietal lobe (L-IPL) was used as a control stimulation condition.ResultsLocal reactivity was significantly associated with working memory and reasoning only after L-PFC stimulation. No associations were found between NfL and cognition. These specific associations were independent of the status of neuroaxonal damage indexed by the NfL biomarker and remained after adjusting for age, biological sex, and education.ConclusionOur results demonstrate that TMS evoked EEG reactivity at the L-PFC, but not the L-IPL, is related to the cognitive status of middle-aged individuals and independent of NfL levels, and may become a valuable biomarker of frontal lobe-associated cognitive function.

The effects of utterance timing and stimulation of left prefrontal cortex on the production of referential expressions

We examined the relationship between the timing of utterance initiation and the choice of referring expressions, e.g., pronouns (it), zeros (…and went down), or descriptive NPs (the pink pentagon). We examined language production in healthy adults, and used anodal transcranial direct current stimulation (tDCS) to test the involvement of the left prefrontal cortex (PFC) in the timing of utterance production and the selection of reference forms in a discourse context. Twenty-two subjects (11 anodal, 11sham) described fast-paced actions, e.g. The gray oval flashes, then it moves right 2 blocks. We only examined trials in contexts that supported pronoun/zero use. For sham participants, pronouns/zeros increased on trials with longer latencies to initiate the target utterance, and trials where the previous trial was short. We argue that both of these conditions enabled greater message pre-planning and greater discourse connectedness: The strongest predictor of pronoun/zero usage was the presence of a connector word like and or then, which was also tended to occur on trials with longer latencies. For the anodal participants, the latency effect disappeared. PFC stimulation appeared to enable participants to produce utterances with greater discourse connectedness, even while planning incrementally.

The effects of utterance timing and stimulation of left prefrontal cortex on the production of referential expressions

The effects of utterance timing and stimulation of left prefrontal cortex on the production of referential expressions

Effects of Unilateral Transcranial Direct Current Stimulation of Left Prefrontal Cortex on Processing and Memory of Emotional Visual Stimuli.

The dorsolateral prefrontal cortex (DLPFC) is generally thought to be involved in affect and emotional processing; however, the specific contribution of each hemisphere continues to be debated. In the present study, we employed unilateral tDCS to test the unique contribution of left DLPFC in the encoding and retrieval of emotional stimuli in healthy subjects. Forty-two right handed undergraduate students received either anodal, cathodal or sham stimulation of left DLPFC while viewing neutral, pleasant, and unpleasant pictures. After completing a filler task, participants were asked to remember as many pictures as possible. Results showed that participants were able to remember a larger amount of emotional (both pleasant and unpleasant) pictures than of neutral ones, regardless of the type of tDCS condition. Participants who received anodal stimulation recalled a significantly higher number of pleasant images than participants in the sham and cathodal conditions, while no differences emerged in the recall of neutral and unpleasant pictures. We conclude that our results provide some support to the role of left prefrontal cortex in the encoding and retrieval of pleasant stimuli.

Left Prefrontal Cortex Contributes to Motor Imagery: A Pilot Study

Transcranial magnetic stimulation (TMS) over the motor cortex during motor imagery results in increased amplitudes of motor evoked potentials (MEPs) in muscles specific to the imagined movement. Functional MRI studies demonstrate that motor imagery involves a widespread neural network including prefrontal and parietal areas. The purpose of this pilot TMS study was to explore whether the left prefrontal cortex (PFC) is an active part of the motor imagery network. MEPs were recorded in 5 healthy subjects in tibialis anterior (TA) muscles during the imagined right ankle dorsiflexion while the neural processes in the left PFC were disturbed by a single TMS pulse 300ms prior to the leg area stimulation with TMS. Motor imagery alone significantly increased MEP amplitudes in the target TA muscle compared to rest(440% on average, p=0.004). The left PFC stimulation prior to test stimulus significantly reduced the facilitation of MEPs during motor imagery (326%, p=0.031) butleft PFC stimulation had no effect when delivered during rest (103%). This suggests a functional link between the left PFC and sensorimotor cortex actively involved in motor imagery. Appropriately timed TMS over the left PCF most likely disturbed the kinesthetic working memory required for maintaining motor imagery.

Efficacy of adjunctive high frequency repetitive transcranial magnetic stimulation of left prefrontal cortex in depression: A randomized sham controlled study

Objective To examine the efficacy of adjunctive left prefrontal high-frequency rTMS treatment in depression patients as compared to sham stimulation. Method 45 right handed moderate to severe depression patients according to ICD-10 DCR criteria were randomized to receive daily sessions of active or sham rTMS (10 Hz, 90% of resting MT, 20 trains, 6 s duration, 1200 pulses/day) over the right dorsolateral prefrontal cortex for 10 days. Depression and psychosis was rated using Structured Interview Guide for the Hamilton Depression Rating Scale (SIGH-D) and Brief Psychiatric Rating Scale (BPRS) respectively before and after rTMS. Result For SIGH-D scores, repeated measures ANOVA showed a significant effect of treatment over time as shown by interaction effect (Pillai's Trace F [1/38] = 56.75, p < .001, η 2 = .60). For BPRS, repeated measures ANOVA showed a significant interaction effect of treatment over time (Pillai's Trace F [1/38] = 39.87, p < .001, η 2 = .51). In psychotic depression patients, repeated measures ANOVA showed a significant effect of treatment over time for SIGH-D scores (Pillai's Trace F [1/25] = 43.04, p<.001, η 2 = .63) and BPRS scores (Pillai's Trace F [1/25] = 42.17, p < .001, η 2 = .63). Conclusion High-frequency left prefrontal rTMS was well tolerated and found to be effective as add-on to standard pharmacotherapy in nonpsychotic as well as psychotic depression.

Within-Session Mood Changes From TMS in Depressed Patients

Within-Session Mood Changes From TMS in Depressed Patients

Chronometry of parietal and prefrontal activations in verbal working memory revealed by transcranial magnetic stimulation

We explored the temporal dynamics of parietal and prefrontal cortex involvement in verbal working memory employing single-pulse transcranial magnetic stimulation (TMS). In six healthy volunteers the left or right inferior parietal and prefrontal cortex was stimulated with the aid of a frameless stereotactic system. TMS was applied at 10 different time points 140–500 ms into the delay period of a two-back verbal working memory task. A choice reaction task was used as a control task. Interference with task accuracy was induced by TMS earlier in the parietal cortex than in the prefrontal cortex and earlier over the right than the left hemisphere. This suggests a propagation of information flow from posterior to anterior cortical sites converging in the left prefrontal cortex. Significant interference with reaction time was observed after 180 ms with left prefrontal cortex stimulation. These effects were not observed in the control task, underlining the task specificity of our results. We propose that the interference with right-sided prefrontal cortex stimulation leads to impaired performance due to disturbed input into the left prefrontal cortex, whereas left-sided TMS interferes directly with the final information processing. Left- and right-sided brain areas might be involved in parallel processing of semantic and object features of the stimuli, respectively.

Mood effects of repetitive transcranial magnetic stimulation of left prefrontal cortex in healthy volunteers

This study investigated the effect of high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) of the left prefrontal cortex (LPFC) on mood in a sham-controlled crossover design. Twenty-five healthy male subjects received HF-rTMS of the LPFC in real and sham conditions. Forty trains (frequency 20 Hz, stimulation intensity 100% of individual motor threshold, train duration 2 s, intertrain interval 28 s) were applied in each session. Mood change from baseline was measured with five visual analog scales (VAS) for sadness, anxiety, happiness, tiredness and pain/discomfort. We were unable to demonstrate significant mood changes from baseline on visual analog scales after either sham or real stimulation of LPFC. There is insufficient evidence to support the general conclusion that HF-rTMS of LPFC has mood effects in healthy volunteers. Future studies should be sham-controlled, have larger sample sizes, and strictly stimulate one single region per session in order to exclude interaction effects with the previous stimulation.