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Biomedical subjects

Felipe Fregni

Publications and source records attributed to Felipe Fregni.

At least 37 records · Page 2Linked to original sources
PubMed2006

Attentional modulation of emotional stimulus processing: an fMRI study using emotional expectancy.

We used emotional expectancy to study attentional modulation in the processing of emotional stimuli. During functional magnetic resonance imaging (fMRI), volunteers saw emotional and neutral expectancy cues signaling the subsequent presentation of corresponding emotional or neutral pictorial stimuli. As a control, emotional and neutral pictures were presented without preceding expectancy cue, resulting in a 2 x 2 factorial design with the factors "expectancy" and "emotion." Statistical analysis revealed a significant positive interaction effect between these factors in the medial prefrontal cortex (MPFC, Brodmann area [BA] 9/10), amygdala, and dorsal midbrain. In all these regions, expectancy augmented the neural response to emotional but not to neutral pictures. Time course analysis of raw data suggests that this augmented activation was not preceded by baseline increases in MPFC and amygdala during the period of emotional expectancy. In a post-scanning session, the paradigm was presented for a second time to allow emotional intensity rating. Again, a significant interaction between expectancy and emotion was observed, with intensity ratings specifically enhanced in emotional photographs preceded by expectancy. There was a positive correlation between intensity ratings and blood oxygenation level-dependent (BOLD) signals in the left amygdala. We conclude that specific components of the emotion network show enhanced activation in response to emotional stimuli when these are preceded by expectancy. This enhancement effect is not present in neutral pictures and might parallel accentuated subjective feeling states.

Adult↗
PubMed2006

Noninvasive cortical stimulation with transcranial direct current stimulation in Parkinson's disease.

Electrical stimulation of deep brain structures, such as globus pallidus and subthalamic nucleus, is widely accepted as a therapeutic tool for patients with Parkinson's disease (PD). Cortical stimulation either with epidural implanted electrodes or repetitive transcranial magnetic stimulation can be associated with motor function enhancement in PD. We aimed to study the effects of another noninvasive technique of cortical brain stimulation, transcranial direct current stimulation (tDCS), on motor function and motor-evoked potential (MEP) characteristics of PD patients. We tested tDCS using different electrode montages [anodal stimulation of primary motor cortex (M1), cathodal stimulation of M1, anodal stimulation of dorsolateral prefrontal cortex (DLPFC), and sham-stimulation] and evaluated the effects on motor function--as indexed by Unified Parkinson's Disease Rating Scale (UPDRS), simple reaction time (sRT) and Purdue Pegboard test--and on corticospinal motor excitability (MEP characteristics). All experiments were performed in a double-blinded manner. Anodal stimulation of M1 was associated with a significant improvement of motor function compared to sham-stimulation in the UPDRS (P < 0.001) and sRT (P = 0.019). This effect was not observed for cathodal stimulation of M1 or anodal stimulation of DLPFC. Furthermore, whereas anodal stimulation of M1 significantly increased MEP amplitude and area, cathodal stimulation of M1 significantly decreased them. There was a trend toward a significant correlation between motor function improvement after M1 anodal-tDCS and MEP area increase. These results confirm and extend the notion that cortical brain stimulation might improve motor function in patients with PD.

Aged↗
PubMed2006

Hand motor recovery after stroke: tuning the orchestra to improve hand motor function.

The motor deficits after stroke are not only the manifestation of the injured brain region, but rather the expression of the ability of the rest of the brain to maintain function. After a lesion in the primary motor cortex, parallel motor circuits might be activated to generate some alternative input to the spinal motoneurons. These parallel circuits may originate from areas such as the contralateral, undamaged primary motor area, bilateral premotor areas, bilateral supplementary motor areas, bilateral somatosensory areas, cerebellum, and basal ganglia. Most importantly, the efferent, cortico-spinal output pathways must be preserved for a desired behavioral result. Most of the recovery of function after a stroke may represent actual relearning of the skills with the injured brain. The main neural mechanisms underlying this relearning process after stroke involve shifts of distributed contributions across a specific neural network (fundamentally the network engaged in skill learning in the healthy). If these notions are indeed correct, then neuromodulatory approaches, such as transcranial magnetic stimulation, targeting these parallel circuits might be useful to limit injury and promote recovery after a stroke. This paper reviews the stroke characteristics that can predict a good recovery and compensations across brain areas that can be implemented after a stroke to accelerate motor function recovery.

Brain Damage, Chronic↗
PubMed2006

Hand function improvement with low-frequency repetitive transcranial magnetic stimulation of the unaffected hemisphere in a severe case of stroke.

Previous research has shown that low-frequency rTMS of the unaffected hemisphere can improve motor function in acute and chronic stroke patients. However, these studies only investigated patients with mild or moderate motor deficits. We report a case of a stroke patient with a severe motor impairment who underwent sham and active repetitive transcranial magnetic stimulation (rTMS) of the unaffected hemisphere and had significantly improved motor function after active, but not after sham, stimulation of the unaffected primary motor cortex. In an additional session of active rTMS, this patient maintained and further enhanced the initial motor improvement. This case report shows that inhibitory rTMS of the unaffected hemisphere can also be beneficial for stroke patients with severe motor deficits and suggests that this approach of noninvasive brain stimulation should be further investigated in this population of patients.

Aged↗
PubMed2006

A controlled clinical trial of cathodal DC polarization in patients with refractory epilepsy.

PURPOSE: To study the effects of cathodal DC polarization in patients with refractory epilepsy and malformations of cortical development (MCDs) as indexed by seizure frequency and epileptiform EEG discharges. METHODS: Nineteen patients with MCDs and refractory epilepsy underwent one session of DC polarization (20 min, 1 mA) targeting the epileptogenic focus. The number of epileptiform discharges (EDs) in the EEG and seizures were measured before (baseline), immediately after, and 15 and 30 days after either sham or active DC polarization. Seizure frequency after the treatment was compared with baseline. RESULTS: Active compared with sham DC polarization was associated with a significant reduction in the number of epileptiform discharges [mean ED reduction of -64.3% (95% CI, -122.5% to -6.0%) for the active treatment group and -5.8% (95% CI, -26.8% to 15.2%) for the sham treatment group]. A trend (p = 0.06) was noted for decrease in seizure frequency after active compared with sham treatment [mean seizure frequency decrease of -44.0% (95% CI, -95.0% to 7.1%) for the active treatment group and -11.1% (95% CI, -22.2% to 44.4%) for the sham treatment group]. CONCLUSIONS: This randomized, controlled study shows that cathodal DC polarization does not induce seizures and is well tolerated in patients with refractory epilepsy and MCDs. Furthermore, the results suggest that this technique might have an antiepileptic effect based on clinical and electrophysiological criteria.

Adult↗
PubMed2006

Comparison between digital subtraction angiography and magnetic resonance angiography in investigation of nonlacunar ischemic stroke in young patients: preliminary results.

PURPOSE: We preliminarily investigated the relevance of performing digital subtraction angiography (DSA) in addition to magnetic resonance angiography (MRA) in definition of ischemic stroke etiology in young patients. METHOD: DSAs and MRAs from 17 young patients with nonlacunar ischemic stroke were blindly analyzed and their impact on stroke management was evaluated. RESULTS: Etiologies were the same considering results of either DSA or MRA in 12/17 cases. In 15/17 patients no changes would have been made in treatment, regardless of the modality of angiography considered. CONCLUSION: These preliminary results suggest that DSA may be redundant in two thirds of ischemic strokes in young patients. Further larger prospective studies are necessary to determine indications of DSA in this age group.

Adolescent↗
PubMed2006

Tinnitus and brain activation: insights from transcranial magnetic stimulation.

The mechanisms underlying tinnitus are still not completely elucidated, but advances in neuroimaging and brain stimulation have provided us with new insights. Evidence suggests that tinnitus might actually be generated by central rather than peripheral structures. To illustrate the importance of brain activity changes in the pathology of tinnitus, we report the cases of 2 patients who experienced a recurrence/worsening of their tinnitus after they had undergone treatment for major depression with repetitive transcranial magnetic stimulation. We suggest that the tinnitus in these 2 patients was induced by changes in brain activity resulting from transcranial magnetic stimulation of the prefrontal cortex. We also review the pathophysiology and other aspects of tinnitus, focusing on associated brain reorganization.

Auditory Cortex↗
PubMed2006

rTMS combined with motor learning training in healthy subjects.

PURPOSE: This study explored the effects of motor learning training combined with repetitive transcranial magnetic stimulation (rTMS) on motor performance in healthy subjects. METHODS: Twenty-seven right-handed subjects were randomized to three groups: ipsilateral rTMS (IS group), contralateral rTMS (CS group), and sham rTMS (SS group). rTMS was applied for 10 minutes (1 Hz, 90% motor threshold) prior to training. Training involved 10 minutes of finger tracking with the right hand. Tracking performance was tested before, during and after training. RESULTS: Improvement in tracking performance over the posttests was not significantly different between the CS and SS groups, whereas it was significantly lower for the IS group compared to the SS group. No difference was found across groups at retention tests. CONCLUSION: These findings indicate that rTMS interfered with motor performance transiently when applied ipsilateral to the training hand and had no effect when applied contralaterally. These results invite further work to determine whether the disruptive effect of ipsilateral rTMS observed here in healthy subjects, with presumably balanced interhemispheric inhibition, might translate differently to subjects with abnormal interhemispheric inhibition (stroke patients) in a way that disinhibits the ipsilesional hemisphere and improves performance in the paretic hand.

Adolescent↗
PubMed2005

Effect of low-frequency transcranial magnetic stimulation on an affective go/no-go task in patients with major depression: role of stimulation site and depression severity.

Repetitive transcranial magnetic stimulation (rTMS) holds promise as a therapeutic tool in major depression. However, a means to assess the effects of a single rTMS session on mood to guide subsequent sessions would be desirable. The present study examined the effects of a single rTMS session on an affective go/no-go task known to measure emotional-cognitive deficits associated with major depression. Ten patients with an acute episode of unipolar major depression and eight partially or completely remitted (improved) patients underwent 1 Hz rTMS over the left and right dorsolateral prefrontal cortex prior to task performance. TMS over the mesial occipital cortex was used as a control. We observed significantly improved performance in depressed patients following right prefrontal rTMS. This beneficial effect declined with decreasing depression severity and tended to reverse in the improved group. Left prefrontal rTMS had no significant effect in the depressed group, but it resulted in impaired task performance in the improved group. Our findings indicate that the acute response of depressed patients to rTMS varies with the stimulation site and depression severity. Further studies are needed to determine whether the present paradigm could be used to predict antidepressant treatment success or to individualize stimulation parameters according to specific pathology.

Antidepressive Agents↗
PubMed2005

Predictors of antidepressant response in clinical trials of transcranial magnetic stimulation.

Although previous clinical trials have suggested that repetitive transcranial magnetic stimulation (rTMS) has a significant antidepressant effect, the results of these trials are heterogeneous. We hypothesized that individual patients' characteristics might contribute to such heterogeneity. Our aim was to identify predictors of antidepressant response to rTMS. We pooled data from six separate clinical trials conducted independently, which evaluated the effects of rapid rTMS of the left dorsolateral prefrontal cortex in patients with major depression. We investigated 195 patients with regard to demographic, depression and treatment characteristics, psychiatric and drug history. Results showed that age and treatment refractoriness were significant negative predictors of depression improvement when adjusting these variables to other significant predictors and confounders. These findings were not confounded by methodological differences from the six studies, as the results were adjusted for the study site. In conclusion TMS antidepressant therapy in younger and less treatment-resistant patients is associated with better outcome.

Adolescent↗
PubMed2005

Dissociable networks for the expectancy and perception of emotional stimuli in the human brain.

William James posited that comparable brain regions were implicated in the anticipation and perception of a stimulus; however, dissociable networks (at least in part) may also underlie these processes. Recent functional neuroimaging studies have addressed this issue by comparing brain systems associated with the expectancy and perception of visual, tactile, nociceptive, and reward stimuli. In the present fMRI study, we addressed this issue in the domain of pictorial emotional stimuli (IAPS). Our paradigm involved the experimental conditions emotional expectancy, neutral expectancy, emotional picture perception, and neutral picture perception. Specifically, the emotional expectancy cue was uncertain in that it did not provide additional information regarding the positive or negative valence of the subsequent picture. Neutral expectancy and neutral picture perception served as control conditions, allowing the identification of expectancy and perception effects specific for emotion processing. To avoid contamination of the perception conditions by the preceding expectancy periods, 50% of the pictorial stimuli were presented without preceding expectancy cues. We found that the emotional expectancy cue specifically produced activation in the supracallosal anterior cingulate, cingulate motor area, and parieto-occipital sulcus. These regions were not significantly activated by emotional picture perception which recruited a different neuronal network, including the amygdala, insula, medial and lateral prefrontal cortex, cerebellum, and occipitotemporal areas. This dissociation may reflect a distinction between anticipatory and perceptive components of emotional stimulus processing.

Adult↗
PubMed2005

Transcranial direct current stimulation of the unaffected hemisphere in stroke patients.

Recovery of function after a stroke is determined by a balance of activity in the neural network involving both the affected and the unaffected brain hemispheres. Increased activity in the affected hemisphere can promote recovery, while excessive activity in the unaffected hemisphere may represent a maladaptive strategy. We therefore investigated whether reduction of the excitability in the unaffected hemisphere by cathodal transcranial direct current stimulation could result in motor performance improvement in stroke patients. We compared these results with excitability-enhancing anodal transcranial direct current stimulation of the affected hemisphere and sham transcranial direct current stimulation. Both cathodal stimulation of the unaffected hemisphere and anodal stimulation of the affected hemisphere (but not sham transcranial direct current stimulation) improved motor performance significantly. These results suggest that the appropriate modulation of bihemispheric brain structures can promote motor function recovery.

Aged↗
PubMed2005

Anodal transcranial direct current stimulation of prefrontal cortex enhances working memory.

Previous studies have claimed that weak transcranial direct current stimulation (tDCS) induces persisting excitability changes in the human motor cortex that can be more pronounced than cortical modulation induced by transcranial magnetic stimulation, but there are no studies that have evaluated the effects of tDCS on working memory. Our aim was to determine whether anodal transcranial direct current stimulation, which enhances brain cortical excitability and activity, would modify performance in a sequential-letter working memory task when administered to the dorsolateral prefrontal cortex (DLPFC). Fifteen subjects underwent a three-back working memory task based on letters. This task was performed during sham and anodal stimulation applied over the left DLPFC. Moreover seven of these subjects performed the same task, but with inverse polarity (cathodal stimulation of the left DLPFC) and anodal stimulation of the primary motor cortex (M1). Our results indicate that only anodal stimulation of the left prefrontal cortex, but not cathodal stimulation of left DLPFC or anodal stimulation of M1, increases the accuracy of the task performance when compared to sham stimulation of the same area. This accuracy enhancement during active stimulation cannot be accounted for by slowed responses, as response times were not changed by stimulation. Our results indicate that left prefrontal anodal stimulation leads to an enhancement of working memory performance. Furthermore, this effect depends on the stimulation polarity and is specific to the site of stimulation. This result may be helpful to develop future interventions aiming at clinical benefits.

Adult↗
PubMed2005

Antiepileptic effects of repetitive transcranial magnetic stimulation in patients with cortical malformations: an EEG and clinical study.

OBJECTIVE: To study the effects of repetitive transcranial magnetic stimulation (rTMS) on epileptic EEG discharges in patients with refractory epilepsy and malformations of cortical development (MCDs). METHODS: Eight patients with MCD and refractory epilepsy underwent 1 session of low-frequency rTMS (0.5 Hz, 600 pulses) focally targeting the MCD. The number of epileptiform discharges (EDs) in the EEG and seizures were measured before (baseline), immediately after as well as 15 and 30 days after rTMS treatment. RESULTS: Stimulation significantly decreased the number of EDs 15 and 30 days after rTMS treatment (mean reduction of 46.4%, 95% CI 12.7-80.2%, and mean reduction of 42.1%, 95% CI 8.2-75.7%, respectively). This was associated with a significant reduction in the number of seizures reported as compared with the 4-week period preceding rTMS (mean reduction of 57.3%, 95% CI 33.1-80.3%, and mean reduction of 51.2%, 95% CI 27.9-74.9%, respectively). CONCLUSION: This open study shows a significant antiepileptic effect of rTMS based on clinical and electrophysiological criteria and supports the therapeutic utility of rTMS for patients with well-localized epileptogenic cortical malformations.

Adolescent↗
PubMed2005

Left prefrontal repetitive transcranial magnetic stimulation impairs performance in affective go/no-go task.

Functional neuroimaging studies have associated affective go/no-go function with lateral prefrontal activation, but they have not established a causal role and have not determined whether one hemisphere is predominantly engaged. In the present study, 11 normal volunteers underwent slow repetitive transcranial magnetic stimulation of the left and right dorsolateral prefrontal cortex, and the occipital cortex prior to performance of a picture-based affective go/no-go task. We found an interfering effect of left prefrontal repetitive transcranial magnetic stimulation compared with both right prefrontal and occipital repetitive transcranial magnetic stimulation. This impairment concerned positive and negative task stimuli to a similar extent, and tended to be greater in shift compared with nonshift blocks. Our findings demonstrate a functionally relevant lateralization of the prefrontal contribution to affective go/no-go tasks.

Adult↗
PubMed2005

Transient disruption of ventrolateral prefrontal cortex during verbal encoding affects subsequent memory performance.

Episodic memory supports conscious remembrance of everyday experience. Prior functional neuroimaging data indicate that episodic encoding during phonological task performance is correlated with activation in bilateral posterior ventrolateral prefrontal cortex (pVLPFC), although uncertainty remains regarding whether these prefrontal regions make necessary contributions to episodic memory formation. Using functional MRI data to guide application of single-pulse transcranial magnetic stimulation (spTMS), this study examined the necessity of left and right pVLPFC for episodic encoding (as expressed through subsequent memory performance). To assess the timing of critical computations, pVLPFC function was transiently disrupted at different poststimulus onset times while subjects made syllable decisions about visually presented familiar and unfamiliar words; subsequent memory for these stimuli was measured. Results revealed that left pVLPFC disruption during encoding of familiar words impaired subsequent memory, expressed as a decline in recognition confidence, with disruption being maximal at 380 ms after stimulus onset. In contrast, right pVLPFC disruption facilitated subsequent memory for familiar words, expressed as an increase in medium confidence recognition, with this facilitation being maximal at 380 ms. Finally, phonological (syllable) decision accuracy was facilitated by right pVLPFC disruption, with this effect being maximal at 340 ms, but was unaffected by left pVLPFC disruption. These findings suggest that left pVLPFC mechanisms onset between 300 and 400 ms during phonological processing of words, with these mechanisms appearing necessary for effective episodic encoding. In contrast, disruption of correlated mechanisms in right pVLPFC facilitates encoding, perhaps by inducing a functional shift in the mechanisms engaged during learning.

Adolescent↗