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1.
Thalamocortical network: a core structure for integrative multimodal vestibular functions.
Brandt, T, Dieterich, M
Current opinion in neurology. 2019;(1):154-164
Abstract
PURPOSE OF REVIEW To apply the concept of nonreflexive sensorimotor and cognitive vestibular functions and disturbances to the current view of separate right and left thalamocortical systems. RECENT FINDINGS The neuronal modules for sensorimotor and cognitive functions are organized in so-called provincial hubs with intracommunity connections that interact task-dependently via connector hubs. Thalamic subnuclei may serve not only as provincial hubs but also in higher order nuclei as connector hubs. Thus, in addition to its function as a cortical relay station of sensory input, the human thalamus can be seen as an integrative hub for brain networks of higher multisensory vestibular function. Imaging studies on the functional connectivity have revealed a dominance of the right side in right-handers at the upper brainstem and thalamus. A connectivity-based parcellation study has confirmed the asymmetrical organization (i.e., cortical dominance) of the parieto-insular vestibular cortex, an area surrounded by other vestibular cortical areas with symmetrical (nondominant) organization. Notably, imaging techniques have shown that there are no crossings of the vestibular pathways in between the thalamic nuclei complexes. Central vestibular syndromes caused by lesions within the thalamocortical network rarely manifest with rotational vertigo. This can be explained and mathematically simulated by the specific coding of unilateral vestibular dysfunction within different cell systems, the angular velocity cell system (rotational vertigo in lower brainstem lesions) in contrast to the head direction cell system (directional disorientation and swaying vertigo in thalamocortical lesions). SUMMARY The structural and functional separation of the two thalamic nuclei complexes allowed a lateralization of the right and left hemispheric functions to develop. Furthermore, it made possible the simultaneous performance of sensorimotor and cognitive tasks, which require different spatial reference systems in opposite hemispheres, for example, egocentric manipulation of objects (handedness) and allocentric orientation of the self in the environment by the multisensory vestibular system.
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2.
Global orientation in space and the lateralization of brain functions.
Dieterich, M, Brandt, T
Current opinion in neurology. 2018;(1):96-104
Abstract
PURPOSE OF REVIEW The functional role of the vestibular system for multisensory orientation and sensorimotor control is reviewed with a special focus on hemispherical lateralization and its consequences for neurological disorders of higher cortical function. RECENT FINDINGS The peripheral and central vestibular systems are bilaterally organized with ipsilateral and contralateral ascending pathways and two multisensory cortical networks in the right and left hemisphere. The vestibular cortical system shows a structural and functional lateralization with a dominance of the right hemisphere in right-handers and the left hemisphere in left-handers. Although the vestibular brainstem pathways are evenly distributed at lower pontine level, an increasing lateralization builds up because of an asymmetric number of pontine and mesencephalic crossing fibers from left to right in right-handers. This vestibular lateralization causes more frequent and more severe disorders of higher sensorimotor dysfunction in lesions of the right hemisphere such as in hemispatial neglect and the pusher syndrome. SUMMARY There is evidence that multisensory higher vestibular functions including large-scale spatial orientation, spatial memory and navigation are dominated by the right temporo-parietal cortex. A beneficial result of lateralization of brain functions in healthy individuals is that it enables the individual to produce a global sensorimotor response even in case of a mismatch of the actual right and left sensory inputs. The consequence for neurology, however, is that lesions in the dominant hemisphere cause more frequently and more severe disorders such as the visuo-spatial hemineglect and the pusher syndrome.
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3.
Examining hand dominance using dynamometric grip strength testing as evidence for overwork weakness in Charcot-Marie-Tooth disease: a systematic review and meta-analysis.
Roberts-Clarke, D, Fornusek, C, Fiatarone Singh, MA, Burns, J, Hackett, DA
International journal of rehabilitation research. Internationale Zeitschrift fur Rehabilitationsforschung. Revue internationale de recherches de readaptation. 2016;(3):189-96
Abstract
This systematic review with a meta-analysis of studies was carried out to evaluate the potential of overwork weakness on the basis of grip strength of dominant and nondominant hands in individuals with Charcot-Marie-Tooth disease (CMT). Numerous electronic databases were searched from the earliest records to February 2016. Studies of any design including participants older than 18 years of age with a confirmed diagnosis of CMT that measured grip strength of both hands using dynamometric testing were eligible for inclusion. Of 12 593 articles identified following removal of duplicates, five articles fulfilled the criteria. A total of 166 participants, mostly with CMT1 or CMT2, were described from the studies included. Hand and finger pinch grip strength for the dominant compared with the nondominant hand was not statistically different. There is no definitive evidence that preferential use of the dominant hand in CMT impairs function relative to the nondominant hand. Thus, robust exercise trials of progressive resistance training are needed to understand the extent of adaptations possible and provide evidence of the safety of such regimens.
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4.
Factors That Affect Physiologic Tremor and Dexterity During Surgery: A Primer for Neurosurgeons.
Fargen, KM, Turner, RD, Spiotta, AM
World neurosurgery. 2016;:384-9
Abstract
INTRODUCTION All individuals have a physiologic tremor that may become more pronounced in periods of stress, stimulant use, or caffeine. There are few publications measuring the effects of these factors on surgeons or trainees and no comprehensive reviews. We sought to review the representative literature. MATERIALS AND METHODS An exhaustive literature search to identify journal articles evaluating factors that affect surgical tremor or dexterity was performed. RESULTS Our search identified 34 studies. All included manuscripts are from small, single-center studies and the vast majority evaluated procedural skills on the basis of laparoscopic simulators. Only one study in which the authors evaluated microsurgical procedural performance was identified. CONCLUSIONS The literature evaluating tremor and its relationship to surgical performance is limited. Surgeons wishing to optimize surgical dexterity may benefit from avoiding caffeine use or fasting before operating and avoiding sleep deprivation or alcohol use the night before procedures. Those surgeons prone to anxiety or stress-related tremor may obtain a benefit from certain beta-blockers. Finally, the use of appropriate surgical ergonomics with hand or wrist steadying may improve surgical tremor and reduce fatigue.
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5.
Abnormal visual field maps in human cortex: a mini-review and a case report.
Haak, KV, Langers, DR, Renken, R, van Dijk, P, Borgstein, J, Cornelissen, FW
Cortex; a journal devoted to the study of the nervous system and behavior. 2014;:14-25
Abstract
Human visual cortex contains maps of the visual field. Much research has been dedicated to answering whether and when these visual field maps change if critical components of the visual circuitry are damaged. Here, we first provide a focused mini-review of the functional magnetic resonance imaging (fMRI) studies that have evaluated the human cortical visual field maps in the face of retinal lesions, brain injury, and atypical retinocortical projections. We find that there is a fair body of research that has found abnormal fMRI activity, but also that this abnormal activity does not necessarily stem from cortical remapping. The abnormal fMRI activity can often be explained in terms of task effects and/or the uncovering of normally hidden system dynamics. We then present the case of a 16-year-old patient who lost the entire left cerebral hemisphere at age three for treatment of chronic focal encephalitis (Rasmussen syndrome) and intractable epilepsy. Using an fMRI retinotopic mapping procedure and population receptive field (pRF) modeling, we found that (1) despite the long period since the hemispherectomy, the retinotopic organization of early visual cortex remained unaffected by the removal of an entire cerebral hemisphere, and (2) the intact lateral occipital cortex contained an exceptionally large representation of the center of the visual field. The same method also indicates that the neuronal receptive fields in these lateral occipital brain regions are extraordinarily small. These features are clearly abnormal, but again they do not necessarily stem from cortical remapping. For example, the abnormal features can also be explained by the notion that the hemispherectomy took place during a critical period in the development of the lateral occipital cortex and therefore arrested its normal development. Thus, caution should be exercised when interpreting abnormal fMRI activity as a marker of cortical remapping; there are often other explanations.
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6.
Peri-ictal water drinking and other ictal vegetative symptoms: Localizing and lateralizing the epileptogenic zone in temporal lobe epilepsy? Two case reports and review of the literature.
Errguig, L, Lahjouji, F, Belaidi, H, Jiddane, M, Elkhamlichi, A, Dakka, T, Ouazzani, R
Revue neurologique. 2013;(11):903-10
Abstract
Peri-ictal behavior disorders can be helpful in localizing and lateralizing seizure onset in partial epilepsies, especially those originating in the temporal lobe. In this paper, we present the case of two right-handed women aged 36 and 42 years who presented with partial seizures of mesial temporal type. Both of the patients had drug resistant epilepsy and undergone presurgical evaluation tests including brain magnetic resonance imaging, video-EEG monitoring and neuropsychological testing. The two patients had hippocampal sclerosis in the right temporal lobe and exhibited PIWD behavior concomitant with right temporal lobe discharges documented during video-EEG recordings. Anterior temporal lobectomy was performed in one case with an excellent outcome after surgery. The patient was free of seizures at 3 years follow-up. We reviewed other publications of peri-ictal autonomic symptoms considered to have a lateralizing significance, such as peri-ictal vomiting, urinary urge, ictal pilo-erection. Clinicians should search for these symptoms, even if not spontaneously reported by the patient, because they are often under-estimated, both by the patients themselves and by physicians. Additionally, patients with lateralizing auras during seizures have a significantly better outcome after epilepsy surgery than those without lateralizing features.
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7.
Diagnostic methods for extra-temporal neocortical focal epilepsies: present and future.
Leite, RA, Otaduy, MC, Silva, GE, Ferreira, ML, Aragão, Mde F
Arquivos de neuro-psiquiatria. 2010;(1):119-26
Abstract
The progress of epilepsies diagnosis has been great, but, amongst the diagnostic detailing that demand research, one of the most important is the essential lateralization and localization of epileptogenic zone, considered as the cerebral cortex region, that removed, will result in a free state of seizures. The present study aims to analyze the possible uses of proton spectroscopy for clinical and pre-surgical evaluation of focal extratemporal epilepsies, since this group presents the highest difficulty degree for lateralizing and locating epileptogenic zones. In almost all cases, a non invasive diagnosis can be performed using routine electroencephalography, video-electroencephalography - considered as gold standard, and magnetic resonance imaging. However, when the results of these exams are contradictory, some patients need invasive techniques, as the intra-cranial video-EEG, using deep electrodes, sub-dural strip and grid, that are associated with increased diagnostic cost and risk of complications, as cerebral hemorrhages and intra-cranial infections. Proton spectroscopy appears as a possibility, given its capacity to evaluate cerebral metabolism, by N-acetyl-aspartate (NAA), creatine (Cre) and choline (Cho) concentrations, amongst other metabolites. This non invasive method may provide time reduction of this evaluation and reliable level improvement for this topographical diagnosis.
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8.
Periodic lateralized epileptiform discharges: Do they represent an ictal pattern requiring treatment?
Hughes, JR
Epilepsy & behavior : E&B. 2010;(3):162-5
Abstract
The goal of this report is to review periodic lateralized epileptiform discharges (PLEDs), particularly their associated symptoms, the possibility that the pattern represents a focal status epilepticus, and finally the usefulness of antiepileptic drugs (AEDs). The associated symptoms often include an "altered state of consciousness" or "confusional state," but also more specific symptoms have been noted, such as nystagmus retractorius, cortical blindness, depression, apraxia, amnesia, hemianopsia, hemiparesis, gaze preference or deviation, dysphasia, and speech impediment. PLEDs have often been referred to as an ictal pattern, and many investigators have viewed the condition an example of subclinical status epilepticus. The intense hypermetabolism and increased blood flow revealed by PET and SPECT scans have been considered to support the ictal nature of this waveform. Although the pattern is difficult to treat, the AEDs that have been reported as successful include carbamazepine, midazolam, pentobarbital, sodium valproate, and felbamate. As only subtle symptoms are, at times, present and therefore may be missed and the pattern is known to be difficult to treat, epileptologists who view the PLED pattern as only an EEG curiosity and decide against treatment may wish to reevaluate the electroclinical evidence related to this interesting and significant pattern.
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9.
Central role of hypothalamic digoxin in conscious perception, neuroimmunoendocrine integration, and coordination of cellular function: relation to hemispheric dominance.
Kurup, RK, Kurup, PA
The International journal of neuroscience. 2002;(6):705-39
Abstract
Alteration in the isoprenoid metabolites--digoxin, ubiquinone, and dolichol--have been reported in neuronal degeneration (Parkinson's disease), oncogenesis (central nervous system glioma), functional neuropsychiatric disorders (schizophrenia and epilepsy), and immune-mediated disorders (multiple sclerosis). The coexistence of these disorders has been documented in literature and a central dysfunction related to digoxin and the isoprenoid pathway may underlie all these disorders. A family with a high prevalence of Parkinson's disease, schizophrenia, neoplasms, syndrome X, rheumatoid arthritis, and epilepsy has been described. The psychological behavioral patterns of the family were: creativity and high IQ, hypersexual behavior, reduced appetite and eating behavior, insomnia and reduced sleep patterns, increased tendency for spirituality, increased tendency for addiction, less bonding and affectionate behavior, and left handedness/right hemispheric dominance. Digoxin, an endogenous Na(+)-K+ ATPase inhibitor secreted by the hypothalamus, was found to be elevated and red blood cell (RBC) membrane Na(+)-K+ ATPase activity was found to be reduced in all the disorders and in the indexed family studied. Hypothalamic digoxin can modulate conscious perception and its dysfunction may lead to schizophrenia. Digoxin can also preferentially upregulate tryptophan transport over tyrosine, resulting in increased levels of depolarizng tryptophan catabolites, serotonin, quinolinic acid, strychnine, and nicotine, and decreased levels of hyperpolarizing tyrosine catabolites, dopamine, noradrenaline, and morphine, contributing to membrane Na(+)-K+ ATPase inhibition in all the above disorders and the indexed family. Digoxin-induced membrane Na(+)-K+ ATPase inhibition can result in increased intracellular Ca2+ and reduced Mg2+ levels, leading on to glutamate excitotoxicity, oncogene activation, and immune activation. Digoxin-induced altered Ca2+/Mg2+ ratios, reduced ubiquinone, and increased dolichol can affect glycoconjugate metabolism, membrane formation and structure, and mitochondrial function, leading to the diverse disorders described above, including those in the indexed family. The isoprenoid pathway and neurotransmitter patterns were compared in right-handed/LH dominant and left-handed/RH dominant individuals. The left-handed/RH dominant individuals compared to right-handed/LH dominant individuals had elevated hydroxymethylglutarylcoenzyme A reductase activity, with increased serum digoxin and dolichol levels. The serum ubiquinone, serum Mg2+ and RBC Na(+)-K+ ATPase activity were reduced in left-handed/RH dominant individuals. The left-handed/RH dominant individuals compared to right-handed/LH dominant individuals had elevated levels of serum tryptophan, quinolinic acid, serotonin, nicotine, and strychnine. The levels of tyrosine, dopamine, noradrenaline, and morphine were low in left-handed/RH dominant compared to right-handed/LH dominant individuals. The hyperdigoxinemic state indicates right hemispheric dominance. Hypothalamic digoxin can thus function as the master conductor of the neuroimmunoendocrine orchestra and coordinate the functions of various cellular organelles.