Claudia Varrasi

Hemispheric asymmetries of cortico-cortical connections in human hand motor areas

OBJECTIVE To evaluate possible functional asymmetries of the motor cortex on the hand-dominant versus the non-dominant hemisphere. METHODS We assessed the handedness of 15 consenting volunteers using the Edinburgh Inventory. They were divided in two groups: 9 right-handers and 6 left-handers. We used single- and paired-transcranial magnetic stimulation (TMS) to measure the relaxed and active motor threshold and the ipsilateral cortico-cortical inhibition and facilitation curve for both hand motor areas. We looked for hemispheric asymmetries of variables related to the side of stimulation (dominant versus non-dominant) and to handedness. RESULTS We found no significant intra- or intergroup hemispheric asymmetry for the relaxed and active thresholds. Among the right-handers, the cortico-cortical inhibition and facilitation curve showed an increased amount of facilitation in the dominant as compared with the non-dominant hand area. No such changes were seen among the left-handers. Both the dominant and the non-dominant hand areas of the right-handers showed more inhibition and less facilitation on the cortico-cortical inhibition and facilitation curve than the corresponding areas of left-handers. CONCLUSION In the right-handers, paired TMS studies showed a functional asymmetry of the motor cortex between the dominant and the non-dominant hand. The left-handers did not show this lateralization. Under TMS investigation their motor cortex function appeared different from that of right-handers.

Slow Repetitive TMS for Drug-resistant Epilepsy: Clinical and EEG Findings of a Placebo-controlled Trial

Summary:  Purpose: To assess the effectiveness of slow repetitive transcranial magnetic stimulation (rTMS) as an adjunctive treatment for drug‐resistant epilepsy.

Cortical Excitability in Cryptogenic Localization‐Related Epilepsy: Interictal Transcranial Magnetic Stimulation Studies

Summary: Purpose: To assess whether single‐ and paired‐pulse transcranial magnetic stimulation (TMS) can measure the interictal brain excitability of medicated patients with cryptogenic localization related epilepsy (CLE). Changes in the balance between excitation and inhibition are the core phenomena in focal epileptogenesis. TMS can assess this balance in the primary motor cortex.

Ketogenic Diet: Electrophysiological Effects on the Normal Human Cortex

Summary:  Purpose: To explore the cortical electrophysiology of the ketogenic diet (KD) in the normal human. KD is effective against refractory epilepsy, but its precise mechanism is obscure. At the transmitter level, an enhancement of GABA inhibition has often been proposed.

Defective visual inhibition in photosensitive idiopathic generalized epilepsy

Purpose:  To assess the visual system excitability of photosensitive patients with idiopathic generalized epilepsy (IGE) with the paired‐pulse flash‐evoked potential (paired F‐VEP) technique.

Accuracy of the ICD-9 codes for identifying TIA and stroke in an Italian automated database

The object of this study was to evaluate the sensitivity and positive predictive value (PPV) of International Classification of Diseases, 9th revision (ICD-9) codes 430–438 in the Sistema Informativo Sanitario Regionale (SISR), an Italian health care automated database. We compared the SISR with a manual search of all cases of transient ischaemic attack (TIA) and stroke discharged from the Novara Hospital, NW Italy. Results were as follows: SISR list: 1017 patients; manual list 1005. Linked: 896; false negatives: 109; false positives: 121. Sensitivity of codes 430–438: 77% at the primary position only and 89% at either the primary or secondary position; PPV: 93% and 88%. Sensitivity and PPV for specific codes vs. each subcategory (sensitivity at the primary position only/any position; PPV at the primary position only/any position): for 430, subarachnoid haemorrhage (33/35%; 46/43%); for 431, cerebral haemorrhage (57/59%; 77/75%); for 434, cerebral infarction (35/37%; 90/87%); for 436, stroke of unknown type (29/29%; 19/16%); and for 435, TIA (75/82%; 80/78%). The SISR database has a high PPV; sensitivity is high for TIA, but low for specific stroke ICD codes.

Effects of a photic input on the human cortico-motoneuron connection

OBJECTIVES Disease manifestations such as photic cortical reflex myoclonus or myoclonus due to intermittent light stimulation rely on a pathologic interaction between non-structured visual inputs and the corticospinal system. We wanted to assess the normal interaction, if any, between a prior photic input and the output of the cortico-motoneuron connection. METHODS In 9 consenting healthy subjects we quantified the changes exerted by a sudden, unexpected bright light flash on (i) the motor potentials (MEPs) evoked in the right first dorsal interosseous muscle (FDI) by transcranial magnetic or electrical stimulation (TMS/TES) of the primary motor cortex, (ii) the FDI F-waves and (iii) the soleus H-wave. Separately, we measured the simple reaction times to the flash itself. All determinations were repeated twice with an interval of 2-24 months. RESULTS When the flash preceded TMS by 55-70 ms, the MEP size was reduced, while at interstimulus intervals (ISIs) of 90-130 ms it was enlarged. Statistical significance (P<0.05) emerged at ISIs of 55, 70, 100, 105 and 120 ms. Conversely, the MEP latency was prolonged at ISIs of 55-70 ms and shortened at ISIs of 90-130 ms (P<0.05 at ISIs of 55, 110 and 130 ms). Electrical MEPs were enhanced at an ISI of 120 ms. The F-wave size showed a non-significant trend of enhancement at ISIs of 90-130 ms. The soleus H-wave showed significant enlargement at ISIs of 90-130 ms (P<0.05 at ISIs of 100 and 105 ms). The minimum reaction time was on average 120 ms. CONCLUSIONS An unexpected photic input, to which no reaction is planned, can cause an early inhibition of the responses to TMS. We think its origin lies within the primary motor cortex, since it is not associated with changes in spinal excitability or electrical MEPs. A later facilitation persists using TES and has a temporal relationship with an enlargement of the soleus H-wave. Thus, it likely results from activation of descending (possibly reticulospinal) fibers that excite the spinal motor nucleus.

The routine circular coil is reliable in paired-TMS studies

OBJECTIVE Motor cortex excitability can be measured by transcranial magnetic stimulation (TMS) using different coil types, but paired-TMS was originally devised with a figure-of-eight coil. We asked whether the most popular, circular coil was suited to the every-day assessment of cortical excitability, particularly paired-TMS indexes, and if it reduced the measurement error. METHODS We studied 12 right-handed, healthy subjects (34±7.6 years). Resting motor threshold (MT), cortical silent period (CSP), short-interval intracortical inhibition (SICI) at the 2, 3, 4 and 5 ms interstimulus intervals (ISIs) and intracortical facilitation (ICF) at the 14 and 16 ms ISIs were measured. Intrinsic variability of these indexes was evaluated in terms of Coefficients of Variation, to estimate the measurement error. This sequence was carried out both using a figure-of-eight coil over the hand motor area and a circular coil centred at the vertex. Testing was repeated 8-13 months later. RESULTS On average, MT, SICI and ICF did not show any statistically significant difference (p>0.05) when studied with the figure-of-eight as compared with the circular coil. CSP was significantly shorter (p=0.007) with the figure-of-eight coil. Using either coil did not affect measurement variability. There was no significant session-to-session group difference at any of the variables using either coil type. CONCLUSIONS Except for the CSP duration, the TMS testing and retesting of cortical excitability, particularly the paired-pulse indexes, did not vary significantly as a function of the coil used. SIGNIFICANCE Routine circular coils can be used reliably in paired-TMS studies designed to measure longitudinal changes in cortical excitability though they do not reduce the measurement error.

Defective Fas‐mediated T‐cell apoptosis predicts acute onset CIDP

Guillain‐Barré syndrome (GBS) and chronic inflammatory demyelinating polyneuropathy (CIDP) are immune‐mediated neuropathies. GBS is characterized by acute onset and subsequent remission of symptoms, whereas CIDP displays slow progression over at least 2 months. However, a small proportion of CIDP patients display acute onset CIDP (a‐CIDP) resembling that of GBS. The Fas receptor is involved in shutting off the immune response and its defective function predisposes to auto‐immune diseases. In CIDP patients, Fas function is lower than in GBS patients and healthy controls. This study is aimed at assessing whether evaluation of T‐cell Fas function helps in early discrimination between GBS and a‐CIDP. Fas function was evaluated in patients with acute onset polyneuropathy: 55 retrospective patients analyzed after development of GBS or a‐CIDP before year 2005; 50 prospective patients analyzed at onset after year 2005 and followed up for development of GBS or a‐CIDP. In both groups, a‐CIDP patients displayed defective Fas function, whereas GBS patients displayed normal function. These findings suggest that the evaluation of Fas function in acute onset polyneuropathy helps in early prediction of long‐term outcome.

Overactive visuomotor connections underlie the photoparoxysmal response. A TMS study.

The photoparoxysmal response (PPR) involves rapid spread of epileptic activity from visual to parietal and frontal areas. We used a transcranial magnetic stimulation (TMS) technique to assess the physiologic connections between primary visual (V1) and motor (M1) areas in patients with idiopathic generalized epilepsy (IGE). We hypothesized that in PPR‐positive patients, M1 would respond excessively to inputs from V1.