The value of navigation-guided rTMS for the treatment of depression: an illustrative case.

Repetitive transcranial magnetic stimulation (rTMS) of the prefrontal cortex has been thought to have great potential to treat refractory depression since the first studies published ten years ago. However, one of the potential limitations of rTMS is the poor definition of the localization of the prefrontal cortical target, which is based on a rather simplistic anatomical approach, i.e., 5cm anterior to the primary motor cortical representation of the hand. This "standard procedure" does not take into consideration interindividual variations in brain morphology. We report the case of a 40-year-old woman who underwent two weeks of 10Hz-rTMS for the treatment of a major, drug-resistant depressive episode. The rTMS target was determined with the "standard procedure" for the first week and with a dedicated navigation system as the left Brodmann area 46 for the second week. The clinical assessment of antidepressant effects was performed before and after each week of stimulation. Following the first week of stimulation, the patient improved, in particular regarding speech production. Using the navigation system, the location of the target stimulated during the first week was found to correspond to Broca's area, and not to the prefrontal area as intended. Antidepressant effects were more marked after the second week of navigated rTMS. In the present case, the prefrontal target was situated 8.3cm anterior to hand motor cortex. This illustrates that the "standard procedure" may inaccurately target the prefrontal cortex, although resulting in antidepressant-like effects. The use of navigation systems should limit the variability of the results reported so far in the treatment of depression by rTMS.

Low-frequency repetitive TMS of premotor cortex can reduce painful axial spasms in generalized secondary dystonia: a pilot study of three patients.

Dystonia is associated with excessive corticospinal motor output. Motor cortex excitability may be reduced by low-frequency repetitive transcranial magnetic stimulation (rTMS) of premotor cortical areas. We report the effects of 1 Hz rTMS applied at 90% of resting motor threshold over the left premotor cortex in an open pilot study of three patients with severe, generalized, secondary dystonia including painful spasms in the proximal and axial musculature. A 20-min session of premotor rTMS was daily performed during 5 consecutive days. The series of rTMS sessions dramatically reduced the painful spasms, for 3-8 days after the last session, without any other significant beneficial effects. However, a slight reduction of the Movement score of the Burke, Fahn and Marsden rating scale was observed for two patients, and of the Disability score for the third one. Low-frequency rTMS of the premotor cortex may improve some specific motor symptoms in severe, generalized dystonia. These results should prompt confirmation in a larger placebo-controlled study.

Cell mechanotransduction and interactions with biological tissues.

The biomechanical mechanisms involved in the processes of tissue remodeling and adaptation are reviewed with emphasis on mechanotransduction at the cellular level. New theoretical models associated with experimental rheological techniques are briefly commented.

Somatotopic organization of the analgesic effects of motor cortex rTMS in neuropathic pain.

BACKGROUND: Motor cortex repetitive transcranial magnetic stimulation (rTMS) was found to relieve chronic neuropathic pain, but the optimal parameters of stimulation remain to be determined, including the site of stimulation. OBJECTIVE: To determine the relationship between cortical stimulation site and pain site regarding the analgesic efficacy of rTMS of motor cortex in chronic neuropathic pain. METHODS: Thirty-six patients with unilateral chronic neuropathic pain located at the face or the hand were enrolled. Motor cortex rTMS was applied at 10 Hz over the area corresponding to the face, hand, or arm of the painful side, whatever pain location. Analgesic effects were daily assessed on visual analogue scale for the week that followed each rTMS session. RESULTS: All types of rTMS session, whatever the target, significantly relieved pain, compared with baseline. However, analgesic effects were significantly better after hand than face area stimulation in patients with facial pain and after face than hand or arm area stimulation in patients with hand pain. CONCLUSION: Repetitive transcranial magnetic stimulation was more effective for pain relief when the stimulation was applied to an area adjacent to the cortical representation of the painful zone rather than to the motor cortical area corresponding to the painful zone itself. This result contradicts the somatotopic efficacy observed for chronic epidural motor cortex stimulation with surgically implanted electrodes.

Stiffening response of a cellular tensegrity model.

Living cells exhibit, as most biological tissues, a stiffening (strain-hardening) response which reflects the nonlinearity of the stress-strain relationship. Tensegrity structures have been proposed as a comprehensive model of such a cell's mechanical response. Based on a theoretical model of a 30-element tensegrity structure, we propose a quantitative analysis of its nonlinear mechanical behavior under static conditions and large deformations. This study provides theoretical foundation to the passage from large-scale tensegrity models to microscale living cells, as well as the comparison between results obtained in biological specimens of different sizes. We found two non-dimensional parameters (L*-normalized element length and T*-normalized elastic tension) which govern the mechanical response of the structure for three types of loading tested (extension, compression and shear). The linear strain-hardening is uniquely observed for extension but differed for the two other types of loading tested. The stiffening response of the theoretical model was compared and discussed with the living cells stiffening response observed by different methods (shear flow experiments, micromanipulation and magnetocytometry).