Hot Spot Hound: a novel robot-assisted platform for enhancing TMS performance

Manipulator Control of the Robotized TMS System with Incurved TMS Coil Case

This paper proposes the force/torque control strategy for the robotized transcranial magnetic stimulation (TMS) system, considering the shape of the TMS coil case. Hybrid position/force control is used to compensate for the error between the current and target position of the coil and to maintain the contact between the coil and the subject’s head. The desired force magnitude of the force control part of the hybrid controller is scheduled by the error between the current and target position of the TMS coil for fast error reduction and the comfort of the subject. Additionally, the torque proportional to the torque acting on the coil’s center is generated to stabilize the contact. Compliance control, which makes the robot adaptive to the environment, stabilizes the coil and head interaction during force/torque control. The experimental results showed that the force controller made the coil generate a relatively large force for a short time (less than 10 s) for the fast error reduction, and a relatively small interaction force was maintained for the contact. They showed that the torque controller made the contact area inside the coil. The experiment also showed that the proposed strategy could be used for tracking a new target point estimated by the neuronavigation system when the head moved slightly.

Evaluation of hand-eye and robot-world calibration algorithms for TMS application

In this paper we compare three approaches to solve the hand-eye and robot-world calibration problem, for their application to a Transcranial Magnetic Stimulation (TMS) system. The selected approaches are: i) non-orthogonal approach (QR24); ii) stochastic global optimization (SGO); iii) quaternion-based (QUAT) method. Performance were evaluated in term of translation and rotation errors, and computational time. The experimental setup is composed of a 7 dof Panda robot (by Franka Emika GmbH) and a Polaris Vicra camera (by Northern Digital Inc) combined with the SofTaxic Optic software (by E.M.S. srl). The SGO method resulted to have the best performance, since it provides lowest errors and high stability over different datasets and number of calibration points. The only drawback is its computational time, which is higher than the other two, but this parameter is not relevant for TMS application. Over the different dataset used in our tests, the small workspace (sphere with radius of 0.05m) and a number of calibration points around 150 allow to achieve the best performance with the SGO method, with an average error of 0.83 ± 0.35mm for position and 0.22 ± 0.12deg for orientation.

The contribution of transcranial magnetic stimulation in the diagnosis and in the management of dementia

Transcranial magnetic stimulation (TMS) is emerging as a promising tool to non-invasively assess specific cortical circuits in neurological diseases. A number of studies have reported the abnormalities in TMS assays of cortical function in dementias. A PubMed-based literature review on TMS studies targeting primary and secondary dementia has been conducted using the key words "transcranial magnetic stimulation" or "motor cortex excitability" and "dementia" or "cognitive impairment" or "memory impairment" or "memory decline". Cortical excitability is increased in Alzheimer's disease (AD) and in vascular dementia (VaD), generally reduced in secondary dementias. Short-latency afferent inhibition (SAI), a measure of central cholinergic circuitry, is normal in VaD and in frontotemporal dementia (FTD), but suppressed in AD. In mild cognitive impairment, abnormal SAI may predict the progression to AD. No change in cortical excitability has been observed in FTD, in Parkinson's dementia and in dementia with Lewy bodies. Short-interval intracortical inhibition and controlateral silent period (cSP), two measures of gabaergic cortical inhibition, are abnormal in most dementias associated with parkinsonian symptoms. Ipsilateral silent period (iSP), which is dependent on integrity of the corpus callosum is abnormal in AD. While single TMS measure owns low specificity, a panel of measures can support the clinical diagnosis, predict progression and possibly identify earlier the "brain at risk". In dementias, TMS can be also exploited to select and evaluate the responders to specific drugs and, it might become a rehabilitative tool, in the attempt to restore impaired brain plasticity.