Abnormal cerebellar processing of the neck proprioceptive information drives dysfunctions in cervical dystonia

The cerebellum can influence the responsiveness of the primary motor cortex (M1) to undergo spike timing-dependent plastic changes through a complex mechanism involving multiple relays in the cerebello-thalamo-cortical pathway. Previous TMS studies showed that cerebellar cortex excitation can block the increase in M1 excitability induced by a paired-associative stimulation (PAS), while cerebellar cortex inhibition would enhance it. Since cerebellum is known to be affected in many types of dystonia, this bidirectional modulation was assessed in 22 patients with cervical dystonia and 23 healthy controls. Exactly opposite effects were found in patients: cerebellar inhibition suppressed the effects of PAS, while cerebellar excitation enhanced them. Another experiment comparing healthy subjects maintaining the head straight with subjects maintaining the head turned as the patients found that turning the head is enough to invert the cerebellar modulation of M1 plasticity. A third control experiment in healthy subjects showed that proprioceptive perturbation of the sterno-cleido-mastoid muscle had the same effects as turning the head. We discuss these finding in the light of the recent model of a mesencephalic head integrator. We also suggest that abnormal cerebellar processing of the neck proprioceptive information drives dysfunctions of the integrator in cervical dystonia.

Cerebellar processing of sensory inputs primes motor cortex plasticity

Plasticity of the human primary motor cortex (M1) has a critical role in motor control and learning. The cerebellum facilitates these functions using sensory feedback. We investigated whether cerebellar processing of sensory afferent information influences the plasticity of the primary motor cortex (M1). Theta-burst stimulation protocols (TBS), both excitatory and inhibitory, were used to modulate the excitability of the posterior cerebellar cortex and to condition an ongoing M1 plasticity. M1 plasticity was subsequently induced in 2 different ways: by paired associative stimulation (PAS) involving sensory processing and TBS that exclusively involves intracortical circuits of M1. Cerebellar excitation attenuated the PAS-induced M1 plasticity, whereas cerebellar inhibition enhanced and prolonged it. Furthermore, cerebellar inhibition abolished the topography-specific response of PAS-induced M1 plasticity, with the effects spreading to adjacent motor maps. Conversely, cerebellar excitation had no effect on the TBS-induced M1 plasticity. This demonstrates the key role of the cerebellum in priming M1 plasticity, and we propose that it is likely to occur at the thalamic or olivo-dentate nuclear level by influencing the sensory processing. We suggest that such a cerebellar priming of M1 plasticity could shape the impending motor command by favoring or inhibiting the recruitment of several muscle representations.

Psychogenic nonepileptic seizures: characterization of two distinct patient profiles on the basis of trauma history

This prospective study investigated and compared psychiatric features of 25 consecutive patients with psychogenic nonepileptic seizures (PNES) on the basis of presence of reported trauma. The "trauma" group comprised 19 patients (76%) and the "no-trauma" group comprised 6 patients (34%). We compared history of PNES, psychiatric comorbidity, alexithymia, and symptoms of dissociation. The study clearly characterized two distinct profiles of patients with PNES on the basis of trauma history. Patients with trauma had at least one psychiatric comorbidity or antecedent (vs 0% in the no-trauma group NT, P<0.001) and a higher median score of dissociation (P<0.001). Patients without trauma had more frequent "frustration situations" as a factor triggering PNES and subsequent sick leaves as perpetuating factors (P=0.001). Trauma antecedents correlated with a high rate of psychiatric comorbidity and a strong dissociative mechanism. Patients without trauma had no psychiatric comorbidity and a weaker dissociative mechanism.

Erythrocyte osmotic fragility and cation concentrations during experimentally induced bovine anaplasmosis

1. The osmotic fragility, the concentrations of Na, K and Ca, the osmolality and the total ATPase activity of bovine erythrocytes from uninfected and Anaplasma marginale-infected bovines were studied in an attempt to correlate these parameters with the decrease in the cellular ATP concentration reported during bovine anaplasmosis. 2. The osmotic fragility found in infected bovine erythrocytes, at 0.52% NaCl, was about two times greater than that observed in non-infected bovines. The increase in osmotic fragility was directly related to the increase in intra-erythrocytic parasitemia. 3. The decrease in ATP concentration reported during bovine anaplasmosis could not be directly related to the increased fragility of these cells. The artificial depletion of erythrocytic ATP did not reproduce the same alteration in the osmotic response to NaCl. 4. The plasmatic and cytoplasmatic concentrations of Na, K and CA did not change significantly during bovine anaplasmosis, whereas the interior of the erythrocytes became hyperosmolal. 5. A. marginale-infected bovine erythrocyte membranes showed an increased ATPase activity when compared to control bovines. Parasite-enriched fractions also presented ATPase activity.