Hypo-excitability of cortical areas in patients affected by Friedreich ataxia: A TMS study
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.
Available from: Sachin S Talathi
- "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. "
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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.
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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.
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ABSTRACT: Friedreich ataxia (FA) is a neurodegenerative disease characterized by progressive nervous system damage resulting in severe disability. Cognitive functions and mood disorders in FA have been studied little and with conflicting results. The aim of this study was to investigate cognitive functions and mood disorders in FA subjects and the role of cognitive rehabilitation therapy (sequential treatments) performed during a scheduled study period. The executive functions of 24 subjects with FA were evaluated over one year during three separate periods of in-hospital rehabilitation. The neuropsychological evaluations performed before and after cognitive therapy did not reveal differences in the mean test scores of the MMSE, the Rey 15-item Memorization Test for long-term memory, Raven's Colored Progressive Matrices, the Phonemic Verbal Fluency Test, the Symbol Digit Modalities Test, or the Zung scale. The mean scores of the Stroop color-word interference task and of the Rey 15-item Memorization Test for short-term memory were increased at the final evaluation. This finding of long-lasting stability of neuropsychological test scores is noteworthy, as it suggests that one-year cognitive rehabilitation therapy (sequential treatments) may at least contribute to reducing cognitive decline. A cognitive rehabilitation therapy in addition to the conventional neuromotor rehabilitation treatment may improve the management of subjects with FA.
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