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Biomedical subjects

A Ragazzoni

Publications and source records attributed to A Ragazzoni.

At least 19 recordsLinked to original sources
PubMed2006

Role of the right dorsal premotor cortex in "physiological" mirror EMG activity.

A distributed cortical network enables the lateralization of intended unimanual movements, i.e., the transformation from a default mirror movement to a unimanual movement. Little is known about the exact functional organization of this "non-mirror transformation" network. Involvement of the right dorsal premotor cortex (dPMC) was suggested because its virtual lesion by high-frequency repetitive transcranial magnetic stimulation (rTMS) increased the excitability of the left primary motor cortex (M1) during unilateral isometric contraction of a left hand muscle (Cincotta et al., Neurosci Lett 367: 189-93, 2004). However, no behavioural effects were observed in that experimental protocol. Here we tested behaviourally twelve healthy volunteers to find out whether focal disruption of the right dPMC by "off-line" One Hz rTMS (900 pulses, 115% of resting motor threshold) enhances "physiological" mirroring. This was measured by an established protocol (Mayston et al., Ann Neurol 45: 583-94, 1999) that quantifies the mirror increase in the electromyographic (EMG) level in the isometrically contracting abductor pollicis brevis (APB) muscle of one hand during brief phasic contractions performed with the APB of the other hand. Mirroring in the right APB significantly increased after real rTMS of the right dPMC. In contrast, no change in mirroring was seen with sham rTMS of the right dPMC, real rTMS of the right M1, or real rTMS of the left dPMC. These findings strongly support the hypothesis that the right dPMC is part of the non-mirror transformation cortical network.

Action Potentials↗
PubMed2002

Bilateral motor cortex output with intended unimanual contraction in congenital mirror movements.

In congenital mirror movements (MM), it is unclear whether the "mirror" motor cortex (M1) produces output during intended unimanual movements. In two patients with MM, the cortical silent period (CSP) was abnormally short after focal transcranial magnetic stimulation (TMS) of either M1, but simultaneous bilateral TMS led to significant CSP lengthening. Thus, it is likely that the shortened CSP after unilateral TMS is caused by output from the nonstimulated M1, suggesting that both M1 produce output with intended unimanual movements in patients with MM.

Adolescent↗
PubMed2002

Congenital hemiparesis: different functional reorganization of somatosensory and motor pathways.

OBJECTIVES: To investigate the reorganization of somatosensory and motor cortex in congenital brain injury. METHODS: We recorded motor evoked potentials (MEPs) following transcranial magnetic stimulation (TMS) and somatosensory evoked potentials (SEPs) in a 41 year old man with severe congenital right hemiparesis but only mild proprioceptive impairment. Brain magnetic resonance imaging showed a large porencephalic cavitation in the left hemisphere mainly involving the frontal and parietal lobes. RESULTS: TMS showed fast-conducting projections from the undamaged primary motor cortex to both hands, whereas MEPs were not elicited from the damaged hemisphere. Left median nerve stimulation evoked normal short-latency SEPs in the contralateral undamaged somatosensory cortex. Right median nerve stimulation did not evoke any SEP in the contralateral damaged hemisphere, but a middle-latency SEP (positive-negative-positive, 39-44-48 ms) in the ipsilateral undamaged hemisphere, with a fronto-central scalp distribution. CONCLUSIONS: Our data show that somatosensory function of the affected arm is preserved, most likely through slow-conducting non-lemniscal connections between the affected arm and ipsilateral non-primary somatosensory cortex. In contrast, motor function was poor despite fast-conducting ipsilateral cortico-motoneuronal output from the primary motor cortex of the undamaged hemisphere to the affected arm. This suggests that different forms of reorganization operate in congenital brain injury and that fast-conducting connections between primary cortex areas and ipsilateral spinal cord are not sufficient for preservation or recovery of function.

Adult↗
PubMed2000

Event-related potentials in patients with total locked-in state due to fulminant Guillain-Barré syndrome.

A series of electrophysiological investigations were performed over a 6-month period in two patients affected by fulminant Guillain-Barré polyradiculoneuropathy, who developed an ascending paralysis leading, within 72 h, to flaccid quadriplegia, internal and external ophthalmoplegia, absence of all brainstem reflexes and no respiratory effort: the clinical state resembled brain death. Brain CTs were normal and spinal fluid examination revealed albuminocytological dissociation. All motor nerves tested were unexcitable, whereas sensory responses were markedly abnormal but present. Sequential EEG recordings revealed normal, partially reactive alpha rhythm in both patients. In one patient, normal auditory event-related potentials (ERPs: peak N1, P2, N2, P3, evoked in an 'oddball' paradigm) and CNV-like potentials could be recorded not earlier than the 20th day into the illness. In earlier recordings, N1 and P2 peaks as well as mismatch negativity (MMN) were present over the frontal and central scalp electrodes. This patient has now partially recovered motor functions and no cognitive defects are present, but he has little recollection of the events occurring in the first 2 weeks spent in the ICU, when he was completely paralyzed. The other patient generated normal N1 and P2 ERP peaks, but no N2, P3 and MMN were detected in a series of recordings. He died without having ever regained appropriate behavioral responses. The ERP abnormalities observed raise the matter of the origin of cognitive dysfunction in patients with severe and prolonged de-efferentation/de-afferentation. ERPs allow monitoring the level of alertness and attention and appear more specific than EEG in identifying a state of awareness in patients in which communication is severely impaired as a consequence of neurological disorders.

Adult↗
PubMed1996

Hand motor cortex activation in a patient with congenital mirror movements: a study of the silent period following focal transcranial magnetic stimulation.

Motor evoked potentials (MEPs) to focal transcranial magnetic stimulation (TMS) have demonstrated that abnormal ipsilateral corticospinal projections are active in patients with congenital mirror movements. In addition, movement-related potentials and PET suggest that an abnormal pattern of motor cortex activation could be associated with an anomaly of the corticospinal tracts. In the present study the silent period (SP) following focal TMS was investigated in a woman with familial congenital mirror movements. Recordings were made from both abductor pollicis brevis (APB) muscles. When focal TMS was delivered during an intended contralateral APB muscle contraction, MEP and SP were bilaterally recorded and SP was significantly shorter than the contralateral SP observed in normal controls. An abnormal bilateral activation of the hand motor cortex can explain our findings. The non-stimulated motor cortex causes an early partial recovery of the background EMG activity when the stimulated motor cortex is still inhibited (beginning as soon as the transcallosal and the short-lasting segmental inhibition are both complete).

Adult↗
PubMed1994

Abnormal projection of corticospinal tracts in a patient with congenital mirror movements.

A 31 year-old woman with familial congenital mirror movements not associated with other neurological defects underwent a detailed neurophysiological evaluation including: voluntary electromyographic activity recorded from upper limbs in response to acoustic stimuli, motor evoked potentials from the thenar muscles to focal transcranial magnetic stimulation, F waves from upper extremities, scalp somatosensory evoked potentials and long-latency responses from thenar muscles to electric stimulation of the median nerve. The results were consistent with the presence of fast-conducting pathways connecting each hand motor cortex with both contra- and ipsilateral spinal motoneurones.

Adult↗
PubMed1993

Electrophysiological study of neurologically asymptomatic HIV1 seropositive patients.

EEGs, brainstem auditory evoked potentials (BAEPs) and auditory event-related potentials (ERPs) were recorded from 33 individuals infected with the human immunodeficiency virus, type 1 (HIV1+ patients: 13 CDC Class II or III; 20 Class IV). All were neurologically asymptomatic, non-demented, and had a past history of intravenous drug abuse. Sixteen age- and sex-matched normals and 10 HIV1- former drug addicts served as controls. Half of the HIV1+ and HIV1- subjects displayed mild EEG anomalies and, except for one HIV1+ patient, BAEPs were normal in both groups. ERPs were normal in all HIV1- subjects but anomalous (longer latencies of components P2, N2, P3; reduced amplitude of P3) in 9 HIV1+ patients (27%), the incidence of such anomalies being higher for Class IV than Class II/III patients. Auditory ERPs proved the most sensitive and specific of these electrophysiological procedures in detecting subclinical central nervous system involvement in HIV1 infection.

Adult↗
PubMed1991

Myotonic dystrophy: an electrophysiological study of cognitive deficits.

Patients with Myotonic Dystrophy (MyD) frequently suffer from a dysfunction of the primary sensory pathways, as documented by abnormalities of short-latency evoked potentials. Impairment of intellectual functions has been less extensively investigated. Short-latency brainstem auditory evoked potentials (BAEPs) as well as long-latency auditory event-related potentials (ERPs) were recorded from 5 female and 6 male patients affected by MyD. A simple discrimination ("oddball") paradigm was used to record ERPs to tones from Fz, Cz, Pz. Both BAEPs and ERPs were significantly altered as compared to normals. BAEP abnormalities were detected in 9 patients and ERP components N2 and P3 were delayed or absent for all patients, who nonetheless correctly discriminated between tones. These data indicate that CNS dysfunction in MyD involves not only primary sensory systems but also neural mechanisms underlying cognitive events and ERP generation.

Acoustic Stimulation↗
PubMed1990

Anesthetic induction with thiopental: its effect on scalp topography of median nerve somatosensory evoked potentials.

The effects on median nerve somatosensory evoked potentials (SEPs) of analgesic doses of fentanyl, meperidine or morphine and of sodium thiopental (STP) anesthesia (4 mg/kg) were tested in 36 surgical patients. We also explored changes in SEP components as a function of their scalp location. Before and after medication, responses were recorded from the scalp overlying the parietal cortex (ipsi- and contralateral to the stimulated arm) and the precentral (contralateral) cortex. None of the three opiates affected SEP latencies or amplitudes. The barbiturate increased the amplitudes of subcortical and early cortical components (N18, N20, P22, P25), whose latencies, however, were not significantly modified. The effect of STP on later SEP cortical components depended on their scalp topography: parietal N33 and P45 underwent significant changes in both latency and amplitude, whereas precentral N30 showed a significant amplitude increase only. Thiopental anesthesia produces clearer short-latency SEP recordings, from both parietal (components N20-P25) and precentral (P22, N30) areas.

Adult↗
PubMed1980

Event-related slow potentials evoked during ankle jerk conditioning in wakefulness and NREM sleep.

Slow cortical potentials related to the ankle jerk and to its conditioning were studied in 40 adults while awake and during NREM sleep. A weak sound (S) was used as conditioned stimulus, while the ankle jerk, evoked either by Achilles tendon percussion (P) or by electrical stimulation of the sciatic nerve (H), served as unconditioned or 'imperative' stimulus. During waking, responses to simple stimuli (S, P, H) were mostly negative. During S-P and S-H pairs, responses to S were mainly negative, resembling the CNV, while these to P or to H became mostly positive, like the CNV resolution or the positive phase of the motor potential. During NREM sleep, responses to simple as well as to paired stimuli showed mostly a biphasic (negative-positive) morphology resembling the K complex. The conditioned slow potential changes obtained by pairing a sound with the ankle jerk therefore seem to be abolished during NREM sleep. This absence of conditioning can be related to the absence of habituation during NREM sleep. In 35% of the cases, however, positive slow waves were evoked by paired sounds during sleep. The possible significance of these phenomena is discussed.

Adult↗