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Neural Prosthetic: Mind Reading. STATS 19 SEM 2. 263057202. Talk 6. Alan L. Yuille. UCLA. Dept. Statistics and Psychology. www.stat.ucla/~yuille Neural Prosthetic. • Basic Idea: • Injury to spinal cord prevents actions. • But patient can still think, or plan, the actions. • If these plans can be decoded by a microchip, then the patient can control a robot limb, or other device. Mind Reading. • Basic Assumption: Mind = Brain. • Brain consists of neurons transmitting information by electrical activity. • All thoughts have neuronal correlates. • If you can decode the activity of neurons, then you can read people’s thoughts. Neural Activity • Decoding neural activity corresponds to mind reading. • But how do neurons encode information? • Two classic viewpoints: 1. The grandmother cell that responds whenever you see your grandmother. 2. Activity encoded by populations of neurons. Neural networks (holistic). Decoding Neurons. • It seems clear that some brain activity is localized in specific areas – e.g. face recognition. • Also some neurons respond to specific stimuli – e.g. to faces but not to dogs. • There might even be a Clinton cell… • There is a lot of plasticity. Motion Planning • Motion Planning : experiments (1990) showed that populations of neurons in the motor cortex predicted the direction of movement. • Better ways to interpret neuronal activity – get monkeys to perform simple tasks, measure neuronal activity, perform Bayesian inference. (Brown University). Plasticity and Feedback Helps • The decoding is used to drive a device. • The monkey gets feedback by observing that the device is not doing what it wanted. • The monkey can somehow correct its thought patterns, so that the decoding works. • Like learning to ride a bicycle. Movement Planning • These movement plans, or thoughts, need not be conscious. • Novel actions usually require conscious thought. • But most common actions do not. • Neuronal correlates of consciousness. Neural Prosthetics. • Only a few Universities have serious neural prosthetics programs. • This talk describes work by Richard Andersen’s Laboratory at Caltech. Figures copied from the lab’s webpage. • Michael Black at Brown University. (Decoding). Goal of Neural Prosthetic System. • Read the • plans from the cortex. Activate an external device. Implanting Electrodes. • Measurement is done by • • inserting electrodes into the cortex. These transmit to an external device. Will the implanted electrodes stay in the right place? Will they cease functioning over time? But the electrodes only need to measure activity (passive). They do not need to stimulate neurons (epilepsy). How to Implant Electrodes? • Neurosurgery: • Deep implants of • electrodes to simulate (treatment for Parkinson’s disease). No pain receptors in the brain. Miniaturized Chip. • Chip must measure • neuronal activity. Action potentials. Where the Output Goes. • Chip implanted inside the brain. • Wires go out and activate external devices. Posterior Parietal Cortex. • Earliest place where the thought to make a movement is made. • Size of little fingernail. • About 50,000,000 neurons. • Others work with motor cortex. But this can atrophy with disuse. Plans made in PPC. Sent to Motor Cortex. Transmitted to Spinal Cord. Cognitive Plans • Planning and Visual Coordinates. • Advantage of PPT. Parietal Reach Region. • Reach, Move Eyes, Grasp. Spatial Representation Known. • Knowing spatial representations makes it easier to read the neuronal code. Neural activity as Monkey Thinks. • Monkey is • trained to perform tasks. Waiting period when monkey plans. Close the Loop by Giving Feedback. • Monkey has • feedback. Monkey can adjust neural activity to improve performance. Improve Recordings. • Moveable Probe • Need to adjust Electrodes to take tissue movement into account. Computer Probe. • Adjust Probes. • 1,000 electrodes. Automatically optimize positions. • Microfluidic drug delivery. To remove scar tissue. Decoding Neural Activity. • Local Field Potentials. Local Field Potentials. • Measure Field Potentials. Tuning of Local Field Potentials. • Local Field Potentials: Decoding LFP’s and Spikes • Decoding. Informatics. • Real Time Decoding. • Analysis is similar to that for speech • • recognition. Information in space and time. Similar techniques can be used. Summary. • Planned movements are represented in the Parietal Reach Region. • Neural decoding enables these plans to be read. • Plasticity of neurons makes this easier, training by feedback. • Implanting device by deep brain surgery. • Output wires control external device.