An Autonomous System for Neural and Physiological Recording and Closed-loop Stimulation in Freely Behaving Animals
Fetz Group, University of Washington
The Neurochip is an autonomous, battery-powered integrated recording, computing and stimulating system that can be borne by freely moving animals. It accomplishes three tasks in real-time:
1) Recording and digitizing neural and physiological signals.
The latest version of the Neurochip (NC3b) can record up to 32 channels with high sampling rate (20Ks/s) and high digital resolution (16 bit) (Intan chip). Recorded signals are stored in an on-board SDRAM card. It supports wide range of recorded/digitized signals. Signals that have been successfully recorded by our group include:
- Single-ended and differential neural signals from the brain and spinal cord (activity of single neurons; local field potentials; electrocorticography, ECoG; and electroencephalography, EEG)
- Single-ended and differential electrical signals from peripheral nerves and muscles (electromyography, EMG)
- Other physiological signals, including electro-cardiography (ECG); electro-oculography (EOG) etc.
- Three-axis acceleration and gyroscope signals (with sensor placed on arm, head, torso etc.)
- Digital triggers from external devices
2) Real-time processing and analysis of signals.
Individual recorded signals typically need to be pre-processed to extract meaningful features from them. Examples of pre-processing algorithms that have been implemented:
- AC/DC coupling
- Differential/Laplacian derivation
- Filtering (low-pass, high-pass, band-pass)
- Rectification, squaring
- Envelope of an oscillatory signal
- Event detection
3) Delivery of multi-channel, open- or closed-loop electrical stimulation.
Recorded signals or extracted features can be used in in various “stimulation decision rules” to determine under which conditions electrical stimuli will be delivered. Examples of stimulation rules that have been implemented to trigger stimulation:
- Occurrence of neuronal spikes of a specific waveform
- Large, oscillatory field potentials
- Increase in power in specific frequency band
- Occurrence of spike during a depolarizing oscillatory wave
- Occurrence of a large, depolarizing oscillatory field potential wave during a specific sleep stage, as determined in real-time by EEG, EMG and EOG criteria
- Occurrence of a preset or random amount of time from the last stimulation event (open-loop stimulation).
When one of the rules for stimulation has been met, stimulation is delivered to a determined output channel (single-ended stimulation) or across two output channels (bipolar stimulation). Stimulation parameters like pulse width, intensity and pulsing frequency are defined by the user. Up to 6 output channels can be independently programed and paired with different rules, stimulation parameters and delivery schedules. Examples of tissues that have been successfully stimulated include: cerebral cortex, subcortical areas (deep brain stimulation), spinal cord, peripheral nerves (musculoskeletal nerves and vagus nerve), and muscles.
The CSNE is using the Neurochip platform in a variety of research projects in freely-behaving nonhuman primates (NHPs) and rats:
- Closed-loop cortical stimulation for induction of cortical plasticity in NHPs
- Closed-loop stimulation of reward centers for operant conditioning of physiological or neural responses in NHPs
- Closed-loop cortical stimulation in conjunction with vagus nerve stimulation (VNS) for augmentation of cortical plasticity in NHPs
- Closed-loop, brain state-dependent, cortical stimulation for studying the effect of sleep stages on cortical plasticity in NHPs
- Closed-loop (EMG- or ECoG-triggered) spinal stimulation for motor rehabilitation in rats with spinal cord injury
- Neural and physiological recordings in NHPs to follow brain activity throughout day/night and wake/sleep cycles
Future developments include:
- Wireless transmission of EMG signals from muscle sensors to the Neurochip
- Wireless triggering of stimulation events from the Neurochip to spinal or peripheral nerve stimulator devices
- Activity-dependent optogenetic stimulation