Answer Happy

(a) A monopolar stimulation electrode is located 20 mm above a 100 mm long motoneuron axon orientated along the z-axis, as shown in Figure 1. The electrode is located mid-way along the axon length, and is located in a homogeneous medium of infinite extent. Starting with an expression for the extracellular potential and using the concept of the activating function determine which regions of the fibre axon between z= 0 mm and z = 100 mm will be depolarised if the stimulation electrode acts as (1) a cathode and (ii) an anode. Sketch the activating function along the fibre in both cases. 400 h =20mm Z 100mm Figure 1 (b) Electrical stimulation of the thalamus has been found to be effective in reducing seizure frequency in patients with epilepsy. You are asked to design a chronically implanted deep brain stimulation system for stimulating the thalamus to reduce seizure frequency. The system should deliver local stimulation with bursts of 160 us duration pulses at a frequency of 200 Hz when a seizure is detected at an array of electrocorticograph electrodes located above the site of the seizures.
Describe the system that you propose including the electrode design (material, contact size, configuration) and a method for triggering the stimulation in response to seizure detection in the electrocorticographic signals. Indicate whether the system will use current-controlled or voltage-controlled stimulation, and how it will be powered. Describe how safety concerns will be accounted for in the design of the stimulus pulse. Note that the safe charge density limit currently recommended by device manufacturers for chronically implanted stimulators is 30 uC cmIn each case, explain your design choices.