Georges A. Ghacibeh

Ipsilateral motor activation during unimanual and bimanual motor tasks

OBJECTIVE To test for the presence and possible asymmetry of ipsilateral motor activation during unimanual and bimanual motor tasks. METHODS Twelve right-handed healthy subjects underwent motor evoked potential (MEP) measurement of one hand (target-hand) while the other hand (task-hand) performed different motor tasks. The target-hand was either at rest (first experiment) or performed a Perdue PegBoard task (second experiment). The task-hand was either at rest, performed a simultaneous pegboard task, or rotated a coin (second experiment). RESULTS In the first experiment, the motor task resulted in significant increase in MEP area in the target-hand, regardless which hand was the task-hand, with a greater increase when the left hand was the task-hand. In the second experiment, ipsilateral motor activation was not present for either hand, however, when the right hand was the task-hand, performance of continuous coin rotation by the right hand resulted in a significant decrease in the MEP area of the left hand. CONCLUSIONS Hemispheric asymmetry and task-dependence of ipsilateral motor cortex activation supports the postulate that motor activity may start bilaterally with subsequent interhemispheric inhibition. Furthermore, in right-handers, the left motor cortex is either more active in ipsilateral hand movements or exerts more effective inhibitory control over the right motor cortex than vice versa. SIGNIFICANCE We suggest that hemispheric asymmetry in ipsilateral motor control is a factor in determining motor dominance in right-handed individuals.

The influence of vagus nerve stimulation on memory.

BackgroundVagus nerve stimulation (VNS) has been shown to improve memory. ObjectiveThe purpose of this study was to learn at which stage of memory formation this influence occurs. MethodsTen subjects who had been implanted with vagus nerve stimulators for the treatment of intractable seizures performed tasks that assessed learning and retention (Hopkins Verbal Learning Test) during actual and sham VNS. ResultsWe found that VNS had no effect on learning but enhanced consolidation, which led to improved retention. ConclusionsThe means by which VNS improves retention is probably related to the increased activity in the nucleus of the tractus solitarius and the locus coeruleus-central adrenergic system that activates the amygdala and increases long-term potentiation in the hippocampus.

Dissociation of neglect subtypes with transcranial magnetic stimulation.

Objective: To identify two forms of hemispatial neglect, attentional and intentional, in healthy volunteers using frontal and parietal repetitive transcranial magnetic stimulation (rTMS). Methods: Ten healthy volunteers performed line bisection tasks while viewing stimuli on closed circuit TV. Direct view of the exploring hand and the target was precluded and the TV monitor guided performance. In the normal condition, the direction of hand movement on the table (workspace) was congruent with that on the monitor, and in the reversed condition, the lateral movement in the workspace occurred in the opposite direction on the monitor. The line bisections were performed in three conditions: without rTMS (control), with right frontal rTMS, and with right parietal rTMS. Results: In the normal condition, both right frontal and right parietal rTMS caused a significant rightward deviation (left hemispatial neglect). In the reversed condition, right frontal rTMS continued to cause rightward deviation in the workspace corresponding to leftward bias on the monitor, whereas right parietal rTMS caused leftward deviation in the workspace, corresponding to rightward bias on the monitor. Conclusions: Right frontal repetitive transcranial magnetic stimulation causes motor–intentional neglect, whereas right parietal repetitive transcranial magnetic stimulation causes sensory–attentional neglect. Alternatively, these findings can also be explained based on a dichotomy related to an egocentric-oriented system.

Progressive affective aprosodia and prosoplegia

The right frontal lobe is important for the expression of emotional prosody, emotional faces, and automatic speech. The authors describe a woman who presented with progressive expressive affective aprosodia, affective prosoplegia, amusia, and loss of automatic speech but with an intact ability to understand emotional prosody and faces as well as express and understand syntactic prosody. MRI showed predominant right frontal cortical atrophy. The authors suggest that this patient has a form of frontotemporal dementia, analogous to primary progressive aphasia but disrupting right frontal lobe–mediated functions.

Effects of Donepezil on Verbal Memory After Semantic Processing in Healthy Older Adults

ObjectiveTo learn if acetylcholinesterase inhibitors alter verbal recall by improving semantic encoding in a double-blind randomized placebo-controlled trial. BackgroundCholinergic supplementation has been shown to improve delayed recall in adults with Alzheimer disease. With functional magnetic resonance imaging, elderly adults, when compared with younger participants, have reduced cortical activation with semantic processing. There have been no studies investigating the effects of cholinergic supplementation on semantic encoding in healthy elderly adults. MethodTwenty elderly participants (mean age 71.5, SD±5.2) were recruited. All underwent memory testing before and after receiving donepezil (5 mg, n=11 or 10 mg, n=1) or placebo (n=8) for 6 weeks. Memory was tested using a Levels of Processing task, where a series of words are presented serially. Subjects were either asked to count consonants in a word (superficially process) or decide if the word was “pleasant” or “unpleasant” (semantically process). ResultsAfter 6 weeks of donepezil or placebo treatment, immediate and delayed recall of superficially and semantically processed words was compared with baseline performance. Immediate and delayed recall of superficially processed words did not show significant changes in either treatment group. With semantic processing, both immediate and delayed recall performance improved in the donepezil group. ConclusionsOur results suggest that when using semantic encoding, older normal subjects may be aided by anticholinesterase treatment. However, this treatment does not improve recall of superficially encoded words.

Effect of vagus nerve stimulation on creativity and cognitive flexibility

OBJECTIVE The purpose of this study was to determine whether vagus nerve stimulation influences cognitive flexibility and creativity. METHODS Ten subjects, in whom vagus nerve stimulators had been implanted for the treatment of intractable seizures, performed tasks that assessed cognitive flexibility (solving anagrams), creativity (Torrance Test), and memory (Hopkins Verbal Learning Test) during actual and sham vagus nerve stimulation. RESULTS Vagus nerve stimulation impaired cognitive flexibility and creativity, but these results could not be explained by the induction of a general encephalopathy because VNS did not impair learning and improved retention. CONCLUSIONS The means by which vagus nerve stimulation impairs cognitive flexibility and creative thinking is probably related to increased activity of the locus coeruleus-central adrenergic system that increases the signal-to-noise ratio and improves the brains ability to attend to sensory input, but decreases its ability to recruit large-scale networks.

Lateralized asymmetry of facial motor evoked potentials

Background: There is considerable evidence that emotions are expressed more intensely on the left side of the face. This asymmetry could reflect a right hemisphere advantage in processing emotional material or an asymmetry in corticobulbar motor systems. Transcranial magnetic stimulation (TMS) was used to test for lateralized asymmetry in the cortical control of muscles of facial expression in the lower face Methods: We administered TMS to the motor cortex of 50 subjects during contraction of bilateral orbicularis oris muscles. We analyzed motor evoked potentials (MEPs) with a repeated measures analysis of variance (ANOVA) using hemisphere stimulated and orbicularis oris side recorded as within subject factors Results: TMS elicited contralateral MEPs in 42 of 50 subjects. Forty of these 42 subjects showed bilateral MEPs. The ANOVA showed a significant main effect of face side, such that MEPs elicited in left face were larger than in right face (p < 0.0001). The analysis also showed a significant interaction between the hemisphere stimulated and face side, such that the difference between contralateral and ipsilateral MEPs with right brain TMS was greater than with left brain TMS (p < 0.0001) Conclusions: The results provide evidence of lateralized asymmetry of corticobulbar projections to muscles of facial expression in the lower face.

Biclustering EEG data from epileptic patients treated with vagus nerve stimulation

We present a pilot study of an application of consistent biclustering to analyze scalp EEG data obtained from epileptic patients undergoing treatment with a vagus nerve stimulator (VNS). The ultimate goal of this study is to develop a physiologic marker for optimal VNS parameters (e.g. output current, signal frequency, etc.) using measures of scalp EEG signals. A time series of STLmax values was computed for each scalp EEG channel recorded from two epileptic patients and used as a feature of the two datasets. The averaged samples from stimulation periods were then separated from averaged samples from non‐stimulation periods by feature selection performed within the consistent biclustering routine.The obtained biclustering results allow us to assume that signals from certain parts of the brain consistently change their characteristics when VNS is switched on and could provide a basis for desirable VNS stimulation parameters. A physiologic marker of optimal VNS effect could greatly reduce the cost, time, an...

Seizure recurrence following epilepsy surgery: Is post-operative EEG helpful?

OBJECTIVES We examined whether the relationship between interictal epileptiform discharges (IED) on post-operative EEG and seizure recurrence after epilepsy surgery was different in patients with neocortical and mesiotemporal resections. METHODS We reviewed the records of 93 consecutive patients who underwent epilepsy surgery at our center and who had adequate post-operative follow-up and a post-operative EEG to determine the type of surgery, the recurrence of seizures and the presence of IED on post-operative EEG. RESULTS Chi-square test revealed that for the entire group, there was a significant relationship between the presence of IED and seizure recurrence. However, this relationship was significant in neocortical surgery but not in mesiotemporal surgery. Time distribution of seizure recurrence revealed that in more than half the cases, seizures recurred with the first 3 months. Time distribution was not influenced by the presence of IED. CONCLUSIONS This study revealed that IED on early post-operative EEG correlate with seizure recurrence in neocortical but not mesiotemporal surgeries and may be used to guide patient counseling in this group of patients.

Optimization of epilepsy treatment with vagus nerve stimulation

Epilepsy is one of the most common chronic neurological disorders that affects close to 50 million people worldwide. Antiepilepsy drugs (AEDs), the main stay of epilepsy treatment, control seizures in two thirds of patients only. Other therapies include the ketogenic diet, ablative surgery, hormonal treatments and neurostimulation. While other approaches to stimulation of the brain are currently in the experimental phase vagus nerve stimulation (VNS) has been approved by the FDA since July 1997 for the adjunctive treatment of intractable partial onset epilepsy with and without secondary generalization in patients twelve years of age or older. The safety and efficacy of VNS have been proven and duplicated in two subsequent double‐blinded controlled studies after two pilot studies demonstrated the feasibility of VNS in man. Long term observational studies confirmed the safety of VNS and that its effectiveness is sustained over time. While AEDs influence seizure thresholds via blockade or modulation of ionic...