Repetitive transcranial magnetic stimulation of the left dorsolateral prefrontal cortex improves probabilistic category learning

Theta burst stimulation over the prefrontal cortex: Effects on cerebral oximetry and cardiovascular measures in healthy humans

Theta Burst Stimulation (TBS) is a non-invasive neurophysiological technique, able to induce changes in synaptic activity. Research suggests that TBS may induce changes in cerebral oxygenation, cerebral blood flow, blood pressure and heart rate but there are conflicting results across studies. Thus, the objective of our sham-controlled study is to evaluate if TBS applied to the dorsolateral prefrontal cortex (DLPFC) of healthy volunteers produces changes in cerebral oximetry, heart rate and blood pressure. Forty-nine volunteers of both sexes were randomly allocated to one of five stimulation groups. Before and after real TBS or sham stimulation, blood pressure, heart rate, and cerebral oxygenation of the volunteers were measured. Cerebral oxygenation values were obtained with a near infra-red spectroscopy system. We found a significant reduction in left cortex oximetry after continuous TBS (cTBS) over the left DLPFC (p = 0.039) and a non-significant reduction in right cortex oximetry (p = 0.052). Right hemisphere inhibition (using cTBS) seemed to originate a significant reduction of 8 mmHg in systolic arterial pressure. No other changes were seen in oximetry, cardiac frequency and diastolic arterial pressure. In our group of normal subjects, cTBS applied to the left DLPFC was able to reduce oxygenation in the left cortex. Right hemisphere inhibition was associated with a significant reduction in systolic pressure.

Enhancement of Motor Recovery through Left Dorsolateral Prefrontal Cortex Stimulation after Acute Ischemic Stroke

BACKGROUND

Two previous studies, which investigated transcranial direct current stimulation (tDCS) use in motor recovery after acute ischemic stroke, did not show tDCS to be effective in this regard. We speculated that additional left dorsolateral prefrontal cortex (DLPFC) stimulation may enhance poststroke motor recovery.

METHODS

In the present randomized clinical trial, 20 acute ischemic stroke patients were recruited. Patients received real motor cortex (M1) stimulation in both arms of the trial. The 2 arms differed in terms of real versus sham stimulation over the left DLPFC. The motor component of the Fugl-Meyer upper extremity assessment (FM) and Action Research Arm Test (ARAT) scores were used to assess primary outcomes, and nonlinear mixed effects models were used for data analyses.

RESULTS

Primary outcome measures improved more and faster among the real stimulation group. During the first days of stimulations, the sham group's FM scores increased by 1.2 per day, while the real group's scores increased by 1.7 per day (P = .003). In the following days, FM improvement decelerated in both groups. Based on the derived models, a stroke patient with a baseline FM score of 15 improves to 32 in the sham stimulation group and to 41 in the real stimulation group within the first month after stroke. Models with ARAT scores yielded nearly similar results. No significant adverse effect was reported.

CONCLUSION

The current study results showed that left DLPFC stimulation in conjunction with M1 stimulation resulted in better motor recovery than M1 stimulation alone.

Facilitating the right but not left DLPFC by TMS decreases truthfulness of object-naming responses

Dorsolateral prefrontal cortex (DLPFC) participates in many mental functions involving cognitive control. This also applies to processes underlying deception. Recently it was shown that, compared to the opposite effect found with left-hemisphere 1-Hz repetitive transcranial magnetic stimulation of the DLPFC, right-hemisphere stimulation decreased the propensity to produce untruthful responses in a subsequent task where subjects had freedom to name presented stimulus-objects either veridically or nonveridically. In a similar experiment, the purpose of the present study was to test whether changing the rTMS protocol from the disrupting to facilitatory type can lead to opposite results. When trains of 10-Hz pulses were delivered to the right DLPFC, propensity to lie increased while similar left-hemisphere DLPFC stimulation did not change the rate of untruthful responses. We can conclude that the way how right DLPFC and other areas functionally associated with it are involved in producing truthful or deliberately deceptive statements about perceived objects considerably depends on what are the parameters of stimulation by which functionality of this system is manipulated.

Does rTMS alter neurocognitive functioning in patients with panic disorder/agoraphobia? An fNIRS-based investigation of prefrontal activation during a cognitive task and its modulation via sham-controlled rTMS

OBJECTIVES

Neurobiologically, panic disorder (PD) is supposed to be characterised by cerebral hypofrontality. Via functional near-infrared spectroscopy (fNIRS), we investigated whether prefrontal hypoactivity during cognitive tasks in PD-patients compared to healthy controls (HC) could be replicated. As intermittent theta burst stimulation (iTBS) modulates cortical activity, we furthermore investigated its ability to normalise prefrontal activation.

METHODS

Forty-four PD-patients, randomised to sham or verum group, received 15 iTBS-sessions above the left dorsolateral prefrontal cortex (DLPFC) in addition to psychoeducation. Before first and after last iTBS-treatment, cortical activity during a verbal fluency task was assessed via fNIRS and compared to the results of 23 HC.

RESULTS

At baseline, PD-patients showed hypofrontality including the DLPFC, which differed significantly from activation patterns of HC. However, verum iTBS did not augment prefrontal fNIRS activation. Solely after sham iTBS, a significant increase of measured fNIRS activation in the left inferior frontal gyrus (IFG) during the phonological task was found.

CONCLUSION

Our results support findings that PD is characterised by prefrontal hypoactivation during cognitive performance. However, verum iTBS as an "add-on" to psychoeducation did not augment prefrontal activity. Instead we only found increased fNIRS activation in the left IFG after sham iTBS application. Possible reasons including task-related psychophysiological arousal are discussed.

Bifrontal tDCS prevents implicit learning acquisition in antidepressant-free patients with major depressive disorder

The findings for implicit (procedural) learning impairment in major depression are mixed. We investigated this issue using transcranial direct current stimulation (tDCS), a method that non-invasively increases/decreases cortical activity. Twenty-eight age- and gender-matched, antidepressant-free depressed subjects received a single-session of active/sham tDCS. We used a bifrontal setup - anode and cathode over the left and the right dorsolateral prefrontal cortex (DLPFC), respectively. The probabilistic classification-learning (PCL) task was administered before and during tDCS. The percentage of correct responses improved during sham; although not during active tDCS. Procedural or implicit learning acquisition between tasks also occurred only for sham. We discuss whether DLPFC activation decreased activity in subcortical structures due to the depressive state. The deactivation of the right DLPFC by cathodal tDCS can also account for our results. To conclude, active bifrontal tDCS prevented implicit learning in depressive patients. Further studies with different tDCS montages and in other samples are necessary.