Similarities Between Somatosensory Cortical Responses Induced via Natural Touch and Microstimulation in the Ventral Posterior Lateral Thalamus in Macaques.

Lost sensations, such as touch, could be restored by microstimulation (MiSt) along the sensory neural substrate. Such neuroprosthetic sensory information can be used as feedback from an invasive brain-machine interface (BMI) to control a robotic arm/hand, such that tactile and proprioceptive feedback from the sensorized robotic arm/hand is directly given to the BMI user. Microstimulation in the human somatosensory thalamus (Vc) has been shown to produce somatosensory perceptions. However, until recently, systematic methods for using thalamic stimulation to evoke naturalistic touch perceptions were lacking. We have recently presented rigorous methods for determining a mapping between ventral posterior lateral thalamus (VPL) MiSt, and neural responses in the somatosensory cortex (S1), in a rodent model (Choi et al., 2016; Choi and Francis, 2018). Our technique minimizes the difference between S1 neural responses induced by natural sensory stimuli and those generated via VPL MiSt. Our goal is to develop systems that know what neural response a given MiSt will produce and possibly allow the development of natural "sensation." To date, our optimization has been conducted in the rodent model and simulations. Here, we present data from simple non-optimized thalamic MiSt during peri-operative experiments, where we used MiSt in the VPL of macaques, which have a somatosensory system more like humans, as compared to our previous rat work (Li et al., 2014; Choi et al., 2016). We implanted arrays of microelectrodes across the hand area of the macaque S1 cortex as well as in the VPL. Multi and single-unit recordings were used to compare cortical responses to natural touch and thalamic MiSt in the anesthetized state. Post-stimulus time histograms were highly correlated between the VPL MiSt and natural touch modalities, adding support to the use of VPL MiSt toward producing a somatosensory neuroprosthesis in humans.

A multi-channel telemetry system for brain microstimulation in freely roaming animals.

A system is described that enables an experimenter to remotely deliver electrical pulse train stimuli to multiple different locations in the brains of freely moving rats. The system consists of two separate components: a transmitter base station that is controlled by a PC operator, and a receiver-microprocessor integrated pack worn on the back of the animals and which connects to suitably implanted brain locations. The backpack is small and light so that small animal subjects can easily carry it. Under remote command from the PC the backpack can be configured to provide biphasic pulse trains of arbitrarily specified parameters. A feature of the system is that it generates precise brain-stimulation behavioral effects using the direct constant-voltage TTL output of the backpack microprocessor. The system performs with high fidelity even in complex environments over a distance of about 300 m. Rat self-stimulation tests showed that this system produced the same behavioral responses as a conventional constant-current stimulator. This system enables a variety of multi-channel brain stimulation experiments in freely moving animals. We have employed it to develop a new animal behavior model ("virtual" conditioning) for the neurophysiological study of spatial learning, in which a rat can be accurately guided to navigate various terrains.

Telemetry system for reliable recording of action potentials from freely moving rats.

Recording single cells from alert rats currently requires a cable to connect brain electrodes to the acquisition system. If no cable were necessary, a variety of interesting experiments would become possible, and the design of other experiments would be simplified. To eliminate the need for a cable we have developed a one-channel radiotelemetry system that is easily carried by a rat. This system transmits a signal that is reliable, highly accurate and can be detected over distances of > or = 20 m. The mobile part of the system has three components: (1) a headstage with built-in amplifiers that plugs into the connector for the electrode array on the rat's head; the headstage also incorporates a light-emitting diode (LED) used to track the rat's position; (2) a backpack that contains the transmitter and batteries (2 N cells); the backpack also provides additional amplification of the single cell signals; and (3) a short cable that connects the headstage to the backpack; the cable supplies power to the headstage amplifiers and the LED, and carries the physiological signals from the headstage to the backpack. By using a differential amplifier and recording between two brain microelectrodes the system can transmit action potential activity from two nearly independent sources. In a future improvement, two transmitters with different frequencies would be used telemeter signals from four microelectrodes simultaneously.

Rat navigation guided by remote control.

Free animals can be 'virtually' trained by microstimulating key areas of their brains.