Hypo-excitability of cortical areas in patients affected by Friedreich ataxia: A TMS study

Università degli Studi di Palermo, Palermo, Sicily, Italy
Journal of the Neurological Sciences (Impact Factor: 2.47). 09/2005; 235(1-2):19-22. DOI: 10.1016/j.jns.2005.03.050
Source: PubMed


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.

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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. "
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