Rainer Paine

Induction of Motor Associative Plasticity in the Posterior Parietal Cortex–Primary Motor Network

There is anatomical and functional connectivity between the primary motor cortex (M1) and posterior parietal cortex (PPC) that plays a role in sensorimotor integration. In this study, we applied corticocortical paired-associative stimuli to ipsilateral PPC and M1 (parietal ccPAS) in healthy right-handed subjects to test if this procedure could modulate M1 excitability and PPC-M1 connectivity. One hundred and eighty paired transcranial magnetic stimuli to the PPC and M1 at an interstimulus interval (ISI) of 8 ms were delivered at 0.2 Hz. We found that parietal ccPAS in the left hemisphere increased the excitability of conditioned left M1 assessed by motor evoked potentials (MEPs) and the input-output curve. Motor behavior assessed by the Purdue pegboard task was unchanged compared with controls. At baseline, conditioning stimuli over the left PPC potentiated MEPs from left M1 when ISI was 8 ms. This interaction significantly attenuated at 60 min after left parietal ccPAS. Additional experiments showed that parietal ccPAS induced plasticity was timing-dependent, was absent if ISI was 100 ms, and could also be seen in the right hemisphere. Our results suggest that parietal ccPAS can modulate M1 excitability and PPC-M1 connectivity and is a new approach to modify motor excitability and sensorimotor interaction.

Mapping different intra-hemispheric parietal-motor networks using twin Coil TMS.

BACKGROUND Accumulating evidence suggests anatomical and functional differences in connectivity between the anterior and posterior parts of the inferior-parietal lobule (IPL) and the frontal motor areas. OBJECTIVE/HYPOTHESIS This study investigates whether different intra-hemispheric parietal-motor interactions can be observed along the anterior-posterior axis of the IPL in the resting human brain. METHODS We use a twin coil transcranial magnetic stimulation technique to test intra-hemispheric interactions between three points adjacent to the intra-parietal sulcus (anterior, central, posterior) and the ipsilateral primary motor cortex (M1) at rest in both hemispheres. RESULTS We found that stimulation of the anterior IPL resulted in an inhibition of the ipsilateral M1 in both hemispheres. Stimulation of the central and posterior IPL resulted in a facilitatory effect on ipsilateral M1 in the left but not for the right hemisphere. Additionally we show that there is considerable inter-subject variability concerning the optimal parietal facilitatory and inhibitory position. CONCLUSIONS The IPL has distinct inhibitory and facilitatory connections to the ipsilateral M1. Whereas inhibitory connections are observed in both hemispheres, facilitatory connections are asymmetric. These parietal-motor networks may represent the basis for the functional differences between these regions in reaching and grasping tasks and mirror the functional asymmetry observed in the motor system. From a practical point of view, we note that the inter-subject variability means that future TMS studies of the parietal area might consider a hot-spot localization similar to the procedures commonly used for M1.

Cortical silent period duration and its implications for surround inhibition of a hand muscle

Surround inhibition is a neural mechanism that assists in the focusing of excitatory drive to muscles responsible for a given movement (agonist muscles) by suppressing unwanted activity in muscles not relevant to the movement (surround muscles). The purpose of the study was to determine the contribution of γ‐aminobutyric acidB receptor‐mediated intracortical inhibition, as assessed by the cortical silent period (CSP), to the generation of surround inhibition in the motor system. Eight healthy adults (five women and three men, 29.8 ± 9 years) performed isometric contractions with the abductor digiti minimi (ADM) muscle in separate conditions with and without an index finger flexion movement. The ADM motor evoked potential amplitude and CSP duration elicited by transcranial magnetic stimulation were compared between a control condition in which the ADM was activated independently and during conditions involving three phases (pre‐motor, phasic, and tonic) of the index finger flexion movement. The motor evoked potential amplitude of the ADM was greater during the control condition compared with the phasic condition. Thus, the presence of surround inhibition was confirmed in the present study. Most critically, the CSP duration of the ADM decreased during the phasic stage of finger flexion compared with the control condition, which indicated a reduction of this type of intracortical inhibition during the phasic condition. These findings indicate that γ‐aminobutyric acidB receptor‐mediated intracortical inhibition, as measured by the duration of the CSP, does not contribute to the generation of surround inhibition in hand muscles.

Efficient and reliable characterization of the corticospinal system using transcranial magnetic stimulation.

Purpose: The purpose of this study is to develop a method to reliably characterize multiple features of the corticospinal system in a more efficient manner than typically done in transcranial magnetic stimulation studies. Methods: Forty transcranial magnetic stimulation pulses of varying intensity were given over the first dorsal interosseous motor hot spot in 10 healthy adults. The first dorsal interosseous motor-evoked potential size was recorded during rest and activation to create recruitment curves. The Boltzmann sigmoidal function was fit to the data, and parameters relating to maximal motor-evoked potential size, curve slope, and stimulus intensity leading to half-maximal motor-evoked potential size were computed from the curve fit. Results: Good to excellent test–retest reliability was found for all corticospinal parameters at rest and during activation with 40 transcranial magnetic stimulation pulses. Conclusions: Through the use of curve fitting, important features of the corticospinal system can be determined with fewer stimuli than typically used for the same information. Determining the recruitment curve provides a basis to understand the state of the corticospinal system and select subject-specific parameters for transcranial magnetic stimulation testing quickly and without unnecessary exposure to magnetic stimulation. This method can be useful in individuals who have difficulty in maintaining stillness, including children and patients with motor disorders.

Probing the interaction of the ipsilateral posterior parietal cortex with the premotor cortex using a novel transcranial magnetic stimulation technique

OBJECTIVE Functional imaging studies have shown that control of planned movement involves a distributed network that involves the premotor (PMv) and posterior parietal cortices (PPC). Similarly, anatomical studies show that these regions are densely interconnected via white matter tracts. We therefore hypothesized that the PPC influence over the motor cortex is partly via a connection with the PMv. METHODS Using a novel three-pulse ipsilateral transcranial magnetic stimulation technique, we preconditioned the PPC (80% RMT) at ISIs from 4-15 ms prior to stimulating the PMv and M1 at ISIs of 4 and 6 ms. RESULTS As previously shown, PMv-M1 paired-pulse stimulation resulted in inhibition of the MEP (90% RMT, 4-6 ms) and PPC-M1 paired-pulse stimulation resulted in facilitation of the MEP (90% RMT, 4-8 ms). PPC-M1 paired-pulse stimulation at 80% RMT preconditioning had no effect on M1. PPC-PMv-M1 stimulation resulted in reversal of inhibition observed with PMv-M1 stimulation at ISIs ranging from 6 to 15 ms. CONCLUSIONS The reversal of inhibition observed with PPC-PMv-M1 stimulation suggests that the parietal connection to the PMv plays a role in the modulation of M1. SIGNIFICANCE This is the first study to stimulate three intrahemispheric regions in order to test a disynaptic connection with M1. The described network may be important in a variety of movement disorders.

Participation of the Classical Speech Areas in Auditory Long-Term Memory

Accumulating evidence suggests that storing speech sounds requires transposing rapidly fluctuating sound waves into more easily encoded oromotor sequences. If so, then the classical speech areas in the caudalmost portion of the temporal gyrus (pSTG) and in the inferior frontal gyrus (IFG) may be critical for performing this acoustic-oromotor transposition. We tested this proposal by applying repetitive transcranial magnetic stimulation (rTMS) to each of these left-hemisphere loci, as well as to a nonspeech locus, while participants listened to pseudowords. After 5 minutes these stimuli were re-presented together with new ones in a recognition test. Compared to control-site stimulation, pSTG stimulation produced a highly significant increase in recognition error rate, without affecting reaction time. By contrast, IFG stimulation led only to a weak, non-significant, trend toward recognition memory impairment. Importantly, the impairment after pSTG stimulation was not due to interference with perception, since the same stimulation failed to affect pseudoword discrimination examined with short interstimulus intervals. Our findings suggest that pSTG is essential for transforming speech sounds into stored motor plans for reproducing the sound. Whether or not the IFG also plays a role in speech-sound recognition could not be determined from the present results.

P1065: Induction of motor associative plasticity in the posterior parietal cortex–primary motor network

before and after the exercise on day 1 (T0, T1) and after the exercise on day 5 (T2). Basketball players attended only to T0 and T1. Results: In FCR of the sedentary group (Fig. 1, amplitude ratios, blue: T0, red: T1, green: T2, bars: standard deviations), there were less short latency afferent inhibition and higher facilitation at T1 (statistically significant at ISI 35 and 50 ms). This effect decreased at T2 despite the increased success rate. Basketball players did not show a facilitation as high as that found in the sedentary group. Conclusion: Short term exercises lead to SMI changes which may function in the early phase of gaining the ability. Continued training provided higher success while the electrophysiological changes was decreasing, possibly by the conversion of the learning process into different mechanisms. Exercising already gained abilities do not produce similar SMI changes.

Failed Attempt With Paired Associative Stimulation to Separate Functional and Organic Dystonia: Stimulation To Separate Functional and Organic Dystonia

can be used as a rescue drug for ALO when the effect of botulinum is not sufficient. In this study, the effect for truly disabling cases, such as COT >10 seconds, was not investigated because the maximum baseline COT was 7.0 seconds. The mechanisms of ALO have not been clearly understood. Previous studies have shown that reduced dopaminergic stimulation in the basal ganglia leads to reflex blink hyperexcitability in PD. Therefore, the corneal sensory input excessively induces reflex blink and produces abnormal contraction of the musculus orbicularis oculi in patients with ALO. As shown in this study, the effect of oxybuprocaine for ALO suggests that the hyperexcitability of reflex blink is an important part of the mechanism of ALO. In conclusion, we demonstrated the prompt effect of oxybuprocaine and the agent could possibly be an additional treatment as a rescue drug for ALO in PD.

Supplementary motor area stimulation for Parkinson disease: A randomized controlled studyAuthor Response

Shirota et al.1 reported a large trial of repetitive TMS of the supplementary motor area (SMA) for PD. Stimulation was given weekly for 8 weeks, with a 3-arm design. The authors did not report baseline Unified Parkinsons Disease Rating Scale (UPDRS) scores and time of medication intake with respect to assessment times. Strong …