Search results for "cortex"
showing 10 items of 1827 documents
Maternal history of reading difficulty is associated with reduced language-related gray matter in beginning readers.
2012
Family history and poor preliteracy skills (referred to here as familial and behavioral risk, respectively) are critical predictors of developmental dyslexia. This study systematically investigated the independent contribution of familial and behavioral risks on brain structures, which had not been explored in past studies. We also examined the differential effects of maternal versus paternal history on brain morphometry, and familial risk dimensionally versus categorically, which were also novel aspects of the study. We assessed 51 children (5 to 6 years of age) with varying degrees of familial and behavioral risks for developmental dyslexia and examined associations with brain morphometry…
Enhancement of human cortico-motoneuronal excitability by the selective norepinephrine reuptake inhibitor reboxetine
2002
It has been proposed that norepinephrine plays a critical role in the modulation of cortical excitability, which in turn is thought to influence functional recovery from brain lesions. The purpose of the present experiments was to determine if it is possible to modulate cortical excitability with the selective norepinephrine reuptake inhibitor reboxetine in intact humans. Recruitment curve and intracortical facilitation, assessed by transcranial magnetic stimulation, were increased after oral intake of 8 and 4 mg reboxetine, in the absence of changes in motor threshold, intracortical inhibition, M-response, F-wave or H-reflex. These results demonstrate that reboxetine enhances cortical exci…
Does the Recruitment of Excitation and Inhibition in the Motor Cortex Differ?
2007
The level of excitability within the motor cortex can be described as a balance between excitation and inhibition, but it is unknown how well both processes correlate. To address this question, the authors measured motor cortical excitability and inhibition in healthy human subjects, comparing the recruitment of motor evoked potentials (MEPs) and the duration of the cortical silent period (CSP) after transcranial magnetic stimulation (TMS). Single-pulse "focal" TMS was applied at intensities varying between 90% and 200% of motor thresholds to the right motor cortex of 15 healthy volunteers. The peak-to peak size of MEP responses and the duration of the CSP were measured in small hand muscle…
The effects of a startle on awareness of action
2003
The execution of a ballistic movement within a reaction time task paradigm is significantly speeded up when an unexpected startling auditory stimulus (SAS) is delivered together with the imperative signal. Using Libet's clock, we investigated whether acceleration involves also the subjective appraisal of the time of task execution. In trials containing the SAS, reaction time shortened to 68.7% of control values. However, subjective judgment of task execution remained a similar time with respect to the imperative signal as in control trials. The dissociation between task execution and its subjective perception indicates the existence of separate circuits for action execution and action aware…
Cerebral potentials elicited by mechanical stimuli to the human leg: influence of artifacts
1992
Mechanical stimulation with a reflex hammer was applied to the quadriceps muscle tendon of healthy volunteers and patients. The time-locked electrical signals were recorded from the scalp. In all cases, reproducible potentials could be recorded, with latencies in a range of 20 ms to 100 ms. The potentials recorded in patients under complete spinal anesthesia were similar to those derived before the anesthesia. In brain dead patients who showed absence of median nerve or posterior tibial nerve SEP, reproducible potentials after mechanical stimuli could be recorded as well. The results suggest that the hammer taps lead to mechanical shock waves which are propagated along the body producing ti…
Subthreshold low frequency repetitive transcranial magnetic stimulation selectively decreases facilitation in the motor cortex
2002
Objective: To investigate the modulatory effect of a subthreshold low frequency repetitive transcranial magnetic stimulation (rTMS) train on motor cortex excitability. Methods: The study consisted of two separate experiments. Subjects received a 10 min long subthreshold 1Hz rTMS train. In the first experiment, (single pulse paradigm), cortical excitability was assessed by measuring the amplitude of motor evoked potentials (MEPs) before and after the rTMS train. In the second experiment, a paired pulse paradigm was employed. Results: Corticospinal excitability, as measured by the MEP amplitude, was reduced by the rTMS train (experiment 1), with a significant effect lasting for about 10 min a…
Modulation of input–output curves by low and high frequency repetitive transcranial magnetic stimulation of the motor cortex
2002
Objectives: Exploring the modulatory effects of different frequencies of repetitive transcranial magnetic stimulation (rTMS) on the excitability of the motor cortex as measured by the input-output curve technique (I-O curve). Methods: Sixteen healthy subjects participated in this experiment. On two different sessions, conducted 1 week apart, rTMS was applied either at a frequency of 20 or 1Hz at 90% of individual motor threshold (MT) for a total of 1600 pulses each. Before and after rTMS, the cortical excitability was assessed by measuring MT and the size of motor evoked potentials (MEPs) collected at different intensities of stimulation. Results: The analysis on the whole population showed…
Dominant vs. nondominant arm advantage in mentally simulated actions in right handers
2013
Although plentiful data are available regarding mental states involving the dominant-right arm, the evidence for the nondominant-left arm is sparse. Here, we investigated whether right-handers can generate accurate predictions with either the right or the left arm. Fifteen adults carried out actual and mental arm movements in two directions with varying inertial resistance (inertial anisotropy phenomenon). We recorded actual and mental movement times and used the degree of their similarity as an indicator for the accuracy of motor imagery/prediction process. We found timing correspondences (isochrony) between actual and mental right arm movements in both rightward (low inertia resistance) …
Median and tibial nerve somatosensory evoked potentials: middle-latency components from the vicinity of the secondary somatosensory cortex in humans
1997
The topography of the middle-latency N110 after radial nerve stimulation suggested a generator in SII. To support this hypothesis, we have tried to identify a homologous component in the tibial nerve SEP (somatosensory evoked potential). Evoked potentials following tibial nerve stimulation (motor + sensory threshold) were recorded with 29 electrodes (bandpass 0.5-500 Hz, sampling rate 1000 Hz). For comparison, the median nerve was stimulated at the wrist. Components were identified as peaks in the global field power (GFP). Map series were generated around GFP peaks and amplitudes were measured from electrodes near map maxima. With median nerve stimulation, we recorded a negativity with a ma…
Dopamine D2/D3 receptor availability and venturesomeness.
2011
The construct of impulsivity is considered as a major trait of personality. There is growing evidence that the mesolimbic dopamine system plays an important role in the modulation of impulsivity and venturesomeness, the two key components within the impulsivity-construct. The aim of the present study was to explore an association between trait impulsivity measured with self-assessment and the dopaminergic neurotransmission as measured by positron emission tomography (PET) in a cohort of healthy male subjects. In vivo D2/D3 receptor availability was determined with [(18)F]fallypride PET in 18 non-smoking healthy subjects. The character trait impulsivity was measured using the Impulsiveness-V…