032708 - March 27, 2008 1: Brain Machine Interface (BMI)...

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March 27, 2008 1: Brain Machine Interface (BMI) Using signals from patient brains to control robotic devices. 1 st thing to do: understand basic representation of the brain - They need to be awake. - Must be animals Move manipulandem in response to light, by juice reward - electrode in brain to measure activity as they make movement 2: Each line is single trial, tick marks represent times of AP 1) Neurons change response when they make movement - Involved in planning movement 2) Response is maximal at certain point - Suppressed at rightward movement Tuning curve- shows fine rate of neuron, rate of AP before movement initiated - Firing rate low for movements near the right or down to the right - Maximal firing rate at around 135-180 degrees or in the region o AKA neuron’s preferred direction - As you move further away from preferred movement, response decreases - Response of one neuron doesn’t specify movement that animal will make o Need multiple neurons to rpresent movement o Next day, neuron nearby has same tuning curve but preferred direction will be different From many neurons, you have population of preferred direction Each neuron gives a volt of its preferred direction 3: Scientist (Giodropolis??) says brain uses vector average. - All neurons combined vectoral average - Each plot at each location reps response of all neurons before animal makes particular movement - Black portion: each line reps single neuron, direction of line reps preferred direction of that neuron and length of line reps strength of that preference - Pointing to opposite direction of red line reps suppressed neurons - Red arrow is close to actual movement (dashed black arrow): average of neurons o There is deviation from actual direction of motion bc we’re only recording from a hundred neurons whereas there are tens of millions in the cortex. o This is why we want large population, to become more reliable and more robust
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Neurons die and go through processes that could modulate the response. From a large population, this wouldn’t affect much and makes it reliable and robust and faster to obtain results 4: Electrode array is different from before (sharp needles): insulated wires, more flexible and blunt. Take an array and press into brain, sits and each wire records wire of one or few neurons near tip of electrode - Record few hundred neurons simultaneously - Implanted for many months, record activity from same regions Can we take signal from electrodes and do what Gerodropolis did before and predict movement in a short period of time? - Need algorithm 5: Train Belle (Duke University) to manipulate manipulandem, microde array measures times of AP/spikes of indiv neurons, computer in nearby room tries to predict next movement. Couple of months later, algorithm got better at predicting what Belle would do.
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032708 - March 27, 2008 1: Brain Machine Interface (BMI)...

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