Cerebral tissue response to electrode implantation

The subthalamic microlesion story in Parkinson's disease: electrode insertion-related motor improvement with relative cortico-subcortical hypoactivation in fMRI

Electrode implantation into the subthalamic nucleus for deep brain stimulation in Parkinson's disease (PD) is associated with a temporary motor improvement occurring prior to neurostimulation. We studied this phenomenon by functional magnetic resonance imaging (fMRI) when considering the Unified Parkinson's Disease Rating Scale (UPDRS-III) and collateral oedema. Twelve patients with PD (age 55.9± (SD)6.8 years, PD duration 9-15 years) underwent bilateral electrode implantation into the subthalamic nucleus. The fMRI was carried out after an overnight withdrawal of levodopa (OFF condition): (i) before and (ii) within three days after surgery in absence of neurostimulation. The motor task involved visually triggered finger tapping. The OFF/UPDRS-III score dropped from 33.8±8.7 before to 23.3±4.8 after the surgery (p<0.001), correlating with the postoperative oedema score (p<0.05). During the motor task, bilateral activation of the thalamus and basal ganglia, motor cortex and insula were preoperatively higher than after surgery (p<0.001). The results became more enhanced after compensation for the oedema and UPDRS-III scores. In addition, the rigidity and axial symptoms score correlated inversely with activation of the putamen and globus pallidus (p<0.0001). One month later, the OFF/UPDRS-III score had returned to the preoperative level (35.8±7.0, p = 0.4).In conclusion, motor improvement induced by insertion of an inactive electrode into the subthalamic nucleus caused an acute microlesion which was at least partially related to the collateral oedema and associated with extensive impact on the motor network. This was postoperatively manifested as lowered movement-related activation at the cortical and subcortical levels and differed from the known effects of neurostimulation or levodopa. The motor system finally adapted to the microlesion within one month as suggested by loss of motor improvement and good efficacy of deep brain stimulation.

Brain–machine interfaces: past, present and future

Since the original demonstration that electrical activity generated by ensembles of cortical neurons can be employed directly to control a robotic manipulator, research on brain-machine interfaces (BMIs) has experienced an impressive growth. Today BMIs designed for both experimental and clinical studies can translate raw neuronal signals into motor commands that reproduce arm reaching and hand grasping movements in artificial actuators. Clearly, these developments hold promise for the restoration of limb mobility in paralyzed subjects. However, as we review here, before this goal can be reached several bottlenecks have to be passed. These include designing a fully implantable biocompatible recording device, further developing real-time computational algorithms, introducing a method for providing the brain with sensory feedback from the actuators, and designing and building artificial prostheses that can be controlled directly by brain-derived signals. By reaching these milestones, future BMIs will be able to drive and control revolutionary prostheses that feel and act like the human arm.

A correlative anatomical and clinical study of pain suppression by deep brain stimulation

The clinical results of electrical stimulation in medial thalamic regions for cancer pain have been correlated with the exact location of the stimulation sites. Five brains were examined by post-mortem histology. Chronic implantation of enamel coated platinum-iridium electrodes for up to 17 months caused relatively mild glial and neuronal reactions and no significant haemorrhage or infarction. The anatomical verifications showed that the electrodes were close to, but not exactly in, the regions defined by the stereotactic coordinates. From the clinico-anatomical correlations it appears that good pain relief can be obtained by electrical stimulation in the periventricular gray region of the posterior thalamus.

Central nervous system reactions to ventriculojugular shunts

The response of the central nervous system (CNS) to ventricular shunts was examined in 19 patients and was found to be similar to the response observed experimentally in animals and in the cases of wound repair in humans. The major finding was the presence of a fibrous capsule surrounding 7 or 12 shunts in place for longer than 2 months. The CNS results differ from those observed in soft tissue responses by the inconstancy of the fibroblastic reaction. The formation of the envelope, when present, is related to hemorrhage secondary to insertion, with no relationship to the duration of shunt use. The ability of tumor cells to spread along the shunt path reflects the weak adhesion between the neural elements and the shunt.