We studied whether the cognitive event-related potentials (ERP) in the subthalamic nucleus (STN) are modified by the modulation
of the inferior frontal cortex (IFC) and the dorsolateral prefrontal cortex (DLPFC) with repetitive transcranial magnetic
stimulation (rTMS). Eighteen patients with Parkinson’s disease who had been implanted with a deep brain stimulation (DBS)
electrode were included in the study. The ERPs were recorded from the DBS electrode before and after the rTMS (1Hz, 600 pulses)
over either the right IFC (10 patients) or the right DLPFC (8 patients). The ERPs were generated by auditory stimuli. rTMS
over the right IFC led to a shortening of ERP latencies from 277±14ms (SD) to 252±19ms in the standard protocol and
from 296±17ms to 270±20ms in the protocol modified by a higher load of executive functions (both P<0.01). The application of rTMS over the DLPFC and the sham stimulation over the IFC showed no significant changes. The
shortening of ERP latency after rTMS over the right IFC reflected the increase in the speed of the cognitive process. The
rTMS modulation of activity of the DLPFC did not influence the ERP. Connections (the IFC-STN hyperdirect pathway) with the
cortex that bypass the BG-thalamocortical circuitries could explain the position of the STN in the processing of executive
"We reported that repetitive transcranial magnetic stimulation (rTMS) of inferior frontal cortex (IFC), but not of dorsolateral prefrontal cortex (DLPFC), increased the speed of processing executive functions (shortening of latencies of event-related potentials) in STN during a dual task performance (Baláz et al., 2010 "
[Show abstract][Hide abstract] ABSTRACT: The modifications of electrophysiological activities of subthalamic nucleus (STN) by non-motor tasks, i.e. movement observation, emotional stimuli and impulse control, were reported repeatedly. Despite being a small structure, STN is apparently involved in a variety of functions. Based on our own electrophysiological recordings and results of other groups we believe that it acts as an indirect modulator which may be involved in tuning the functional systems. STN may modulate specific cognitive activities via contextual modulation of certain cortical areas. Our findings support the hypothesis of a cortical-STN bypass (via hyperdirect pathway) of "classical'' basal ganglia-thalamocortical circuitry, at least during the processing of certain cognitive functions. The modulation of cognitive functions appears to be selective, probably determined by the involvement of cortical neuronal populations interconnected with STN. There could also exist a spatial overlap of areas within STN regulating various functions. That may explain the fact that some non-motor symptoms of Parkinson's disease may improve after deep brain stimulation of STN. These improvements are likely caused by combination of direct stimulation effect on non-motor function and overall beneficial effect of motor improvement on quality of life.
"We previously showed that rTMS applied over the IFG enhanced cognitive speed in a group (n = 10) of non-demented Parkinson's disease (PD) subjects regardless of cognitive load . In the same vein, rTMS applied over the right IFG decreased the latency of P3 waves recorded in the subthalamic nucleus of PD subjects during both simple and dual executive tasks . We hypothesized that similar aftereffects would be achieved in our AD group. "
[Show abstract][Hide abstract] ABSTRACT: Introduction: Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive tool for modulating cortical activity.
Objectives: In this pilot study, we evaluated the effects of high frequency rTMS applied over the right inferior frontal gyrus (IFG) on cognitive functions in patients with amnestic mild cognitive impairment (MCI) or incipient dementia due to Alzheimer’s disease (AD).
Methods: Ten patients (6 men; 4 women, mean age 72 ± 8 years; MMSE 23 ± 3.56) were enrolled in a randomized, placebo-controlled study with a crossover design. All participants received 3 sessions of 10 Hz rTMS over the non-dominant right hemisphere in random order: IFG (active stimulation site) and vertex (control stimulation site). Intensities were adjusted to 90% of resting motor threshold. A total of 2250 pulses were applied in a session. The Trail Making Test (TMT), the Stroop test, and the complex visual scene encoding task (CVSET) were administered before and immediately after each session. The Wilcoxon paired test was used for data analysis.
Results: Stimulation applied over the IFG induced improvement in the TMT parts A (p = 0.037) and B (p = 0.049). No significant changes were found in the Stroop test or the CVSET after the IFG stimulation. We observed no significant cognitive aftereffects of rTMS applied over the vertex.
Conclusions: High frequency rTMS of the right IFG induced significant improvement of attention and psychomotor speed in patients with MCI/mild dementia due to AD. This pilot study is part of a more complex protocol and ongoing research.
Journal of the Neurological Sciences 08/2014; 346(1-2). DOI:10.1016/j.jns.2014.08.036 · 2.47 Impact Factor
"It has been clearly shown that rTMS induces changes of cortical plasticity of motor cortices . The positive effects of TMS on cognitive P300 event-related potential have also been well documented  . Although this may provide a rationale for using the rTMS as a therapeutic tool it is still not easy to estimate how and if the altered mechanism of brain plasticity can serve as a model for developing effective protocols . "
[Show abstract][Hide abstract] ABSTRACT: Repetitive transcranial magnetic stimulation (rTMS) represents a promising tool for studying and influencing cognition in people with neurodegenerative diseases. This procedure is noninvasive and painless, and it does not require the use of anesthesia or pharmacological substances. In this systematic critical review we report outcomes from research focused on behavioral cognitive effects induced by rTMS in patients with Alzheimer's disease (AD), Parkinson's disease (PD), and mild cognitive impairment (MCI) preceding AD. There are still major limitations to rTMS use, such as a poor understanding of its after-effects and inter-individual variability in their magnitude, discrepancies in stimulation protocols and study designs, varied selection of the specific stimulated areas and control procedures, and neuropsychological methods for assessment of after-effects; hence, the results of the present research can only be considered preliminary. The future directions are discussed.
Journal of the neurological sciences 02/2014; 339(1-2). DOI:10.1016/j.jns.2014.01.037 · 2.47 Impact Factor
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