Hypo-excitability of cortical areas in patients affected by Friedreich ataxia: A TMS study
ABSTRACT The aim of the study was to explore excitability of a motor and a non-motor (visual) area in patients affected by Friedreich ataxia and to correlate neurophysiological data with clinical parameters. Seven patients (3M/4F) and ten healthy controls (5M/5F) participated in the study. The hot-spot for activation of right abductor pollicis brevis was checked by means of a figure-of-eight coil and the motor threshold (MT) on this point was recorded. The phosphene threshold (PT) was measured by means of a focal coil over the occipital cortex as the lower intensity of magnetic stimulation able to induce the perception of phosphenes. The patients showed a significantly higher mean PT (p<.03) and MT values (p<.001) than controls. In all but one patient unable to perceive phosphenes (42% vs. 50% of controls), TMS at 100% intensity did not elicit motor response at rest. The difference in percentage of patients (57.1%) and controls (100%) with motor responses was nearly significant. The size of GAA1 expansion showed significant correlations with PT and MT values. The results of our study showed that FA patients had reduced cortical activation, involving both the motor and the visual cortex. The cortical involvement in these patients seems to be mainly genetically determined. The study provides the first evidence of cortical dysfunction in patients with genetically defined Friedreich ataxia.
- SourceAvailable from: Sachin S Talathi
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- "It has been suggested that a tight control of excitatory–inhibitory balance is needed to regulate cortical activity in healthy subjects (Le Roux et al. 2006). This control prevents saturation that may result in disorders associated with hyper-or hypo-excitability such as epilepsy and Friedreich ataxia (Treiman 2001; Brighina et al. 2004). Homeostatic synaptic plasticity (HSP) is a mechanism of recent scientific interest for its role in maintaining the excitatory–inhibitory balance. "
ABSTRACT: Recent experimental results by Talathi et al. (Neurosci Lett 455:145-149, 2009) showed a divergence in the spike rates of two types of population spike events, representing the putative activity of the excitatory and inhibitory neurons in the CA1 area of an animal model for temporal lobe epilepsy. The divergence in the spike rate was accompanied by a shift in the phase of oscillations between these spike rates leading to a spontaneous epileptic seizure. In this study, we propose a model of homeostatic synaptic plasticity which assumes that the target spike rate of populations of excitatory and inhibitory neurons in the brain is a function of the phase difference between the excitatory and inhibitory spike rates. With this model of homeostatic synaptic plasticity, we are able to simulate the spike rate dynamics seen experimentally by Talathi et al. in a large network of interacting excitatory and inhibitory neurons using two different spiking neuron models. A drift analysis of the spike rates resulting from the homeostatic synaptic plasticity update rule allowed us to determine the type of synapse that may be primarily involved in the spike rate imbalance in the experimental observation by Talathi et al. We find excitatory neurons, particularly those in which the excitatory neuron is presynaptic, have the most influence in producing the diverging spike rates and causing the spike rates to be anti-phase. Our analysis suggests that the excitatory neuronal population, more specifically the excitatory to excitatory synaptic connections, could be implicated in a methodology designed to control epileptic seizures.Biological Cybernetics 03/2010; 102(5):427-40. DOI:10.1007/s00422-010-0376-8 · 1.93 Impact Factor
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ABSTRACT: The purpose of this special communication is to provide an overview of noninvasive cortical stimulation techniques, the types of mechanistic information they can provide, and the ways their use is contributing to our understanding of current models of neurorehabilitation. The focus is primarily on studies using noninvasive cortical stimulation techniques in the human motor system. Noninvasive cortical stimulation techniques are useful tools in the field of neurorehabilitation that are being actively used to test proposed models of functional recovery after neurologic injury. They can provide insight into the physiologic mechanisms of functional recovery and are under investigation as a possible auxiliary intervention to modulate cortical excitability and enhance training effects.Archives of Physical Medicine and Rehabilitation 01/2007; 87(12 Suppl 2):S84-93. DOI:10.1016/j.apmr.2006.08.330 · 2.44 Impact Factor
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ABSTRACT: ARTICLE TITLE AND BIBLIOGRAPHIC INFORMATION: Periodontitis and inflammatory markers in transplant recipients. Shaqman M, Ioannidou E, Burleson J, Hull D, Dongari-Bagtzogou A. J Periodontol 2010;81(5):666-72. REVIEWER: Michael P. Rethman, DDS, MS. PURPOSE/QUESTION: Does the presence of severe chronic periodontitis or, alternately, individual signs of chronic periodontitis increase serum indicators of systemic inflammation among solid organ implant patients? SOURCE OF FUNDING: National Institute of Dental and Craniofacial Research (NIDCR grant #R21DE16466). TYPE OF STUDY/DESIGN: Cross-sectional study. LEVEL OF EVIDENCE: Level 2: Limited-quality, patient-oriented evidence. STRENGTH OF RECOMMENDATION GRADE: Not applicable.The journal of evidence-based dental practice 12/2010; 10(4):257-8. DOI:10.1016/j.jebdp.2010.09.010