Telemetric recording of neuronal activity

Wireless and battery-free technologies for neuroengineering

Tethered and battery-powered devices that interface with neural tissues can restrict natural motions and prevent social interactions in animal models, thereby limiting the utility of these devices in behavioural neuroscience research. In this Review Article, we discuss recent progress in the development of miniaturized and ultralightweight devices as neuroengineering platforms that are wireless, battery-free and fully implantable, with capabilities that match or exceed those of wired or battery-powered alternatives. Such classes of advanced neural interfaces with optical, electrical or fluidic functionality can also combine recording and stimulation modalities for closed-loop applications in basic studies or in the practical treatment of abnormal physiological processes.

Audio-vocal interactions during vocal communication in squirrel monkeys and their neurobiological implications

Several strategies have evolved in the vertebrate lineage to facilitate signal transmission in vocal communication. Here, I present a mechanism to facilitate signal transmission in a group of communicating common squirrel monkeys (Saimiri sciureus sciureus). Vocal onsets of a conspecific affect call initiation in all other members of the group in less than 100 ms. The probability of vocal onsets in a range of 100 ms after the beginning of a vocalization of another monkey was significantly decreased compared to the mean probability of call onsets. Additionally, the probability for vocal onsets of conspecifics was significantly increased just a few hundreds of milliseconds after call onset of others. These behavioral data suggest neural mechanisms that suppress vocal output just after the onset of environmental noise, such as vocalizations of conspecifics, and increase the probability of call initiation of group mates shortly after. These findings add new audio-vocal behaviors to the known strategies that modulate signal transmission in vocal communication. The present study will guide future neurobiological studies that explore how the observed audio-vocal behaviors are implemented in the monkey brain.

Wireless multi-channel single unit recording in freely moving and vocalizing primates

The ability to record well-isolated action potentials from individual neurons in naturally behaving animals is crucial for understanding neural mechanisms underlying natural behaviors. Traditional neurophysiology techniques, however, require the animal to be restrained which often restricts natural behavior. An example is the common marmoset (Callithrix jacchus), a highly vocal New World primate species, used in our laboratory to study the neural correlates of vocal production and sensory feedback. When restrained by traditional neurophysiological techniques marmoset vocal behavior is severely inhibited. Tethered recording systems, while proven effective in rodents pose limitations in arboreal animals such as the marmoset that typically roam in a three-dimensional environment. To overcome these obstacles, we have developed a wireless neural recording technique that is capable of collecting single-unit data from chronically implanted multi-electrodes in freely moving marmosets. A lightweight, low power and low noise wireless transmitter (headstage) is attached to a multi-electrode array placed in the premotor cortex of the marmoset. The wireless headstage is capable of transmitting 15 channels of neural data with signal-to-noise ratio (SNR) comparable to a tethered system. To minimize radio-frequency (RF) and electro-magnetic interference (EMI), the experiments were conducted within a custom designed RF/EMI and acoustically shielded chamber. The individual electrodes of the multi-electrode array were periodically advanced to densely sample the cortical layers. We recorded single-unit data over a period of several months from the frontal cortex of two marmosets. These recordings demonstrate the feasibility of using our wireless recording method to study single neuron activity in freely roaming primates.

Autonomous head-mounted electrophysiology systems for freely behaving primates

Recent technological advances have led to new light-weight battery-operated systems for electrophysiology. Such systems are head mounted, run for days without experimenter intervention, and can record and stimulate from single or multiple electrodes implanted in a freely behaving primate. Here we discuss existing systems, studies that use them, and how they can augment traditional, physically restrained, 'in-rig' electrophysiology. With existing technical capabilities, these systems can acquire multiple signal classes, such as spikes, local field potential, and electromyography signals, and can stimulate based on real-time processing of recorded signals. Moving forward, this class of technologies, along with advances in neural signal processing and behavioral monitoring, have the potential to dramatically expand the scope and scale of electrophysiological studies.

Automated testing of cognitive performance in monkeys: use of a battery of computerized test systems by a troop of semi-free-ranging baboons (Papio papio)

Fagot and Paleressompoulle (2009) published an automated learning device for monkeys (ALDM) to test the cognitive functions of nonhuman primates within their social groups, but the efficiency of the ALDM procedure with large groups remains unknown. In the present study, 10 ALDM systems were provided ad lib to a troop of 26 semi-free-ranging baboons that were initially naive with computerized testing. The test program taught baboons to solve two-alternative forced choice (2AFC) and matching-to-sample (MTS) tasks. A million trials were recorded for the group during a period of 85 days (Experiment 1). Their analysis shows that 75% of the baboons participated at high frequencies and quickly learned the 2AFC and MTS tasks. In Experiment 2, we compared the baboons' behavior when the ADLM systems were either accessible or closed. ALDM reduced frequencies of object-directed behaviors, but had no overt consequence on social conflicts. In Experiment 3, we tested the process of the global or local attributes of visual stimuli in MTS-trained baboons in order to illustrate the efficiency of ALDM for behavioral studies requiring complex experimental designs. Altogether, the results of the present study validate the use of ALDM to efficiently test monkeys in large social groups. ALDM has a strong potential for a variety of scientific disciplines, including for biomedical research. Supplemental materials for this article may be downloaded from http://brm.psychonomic-journals.org/content/supplemental.

HermesD: A High-Rate Long-Range Wireless Transmission System for Simultaneous Multichannel Neural Recording Applications

HermesD is a high-rate, low-power wireless transmission system to aid research in neural prosthetic systems for motor disabilities and basic motor neuroscience. It is the third generation of our "Hermes systems" aimed at recording and transmitting neural activity from brain-implanted electrode arrays. This system supports the simultaneous transmission of 32 channels of broadband data sampled at 30 ks/s, 12 b/sample, using frequency-shift keying modulation on a carrier frequency adjustable from 3.7 to 4.1 GHz, with a link range extending over 20 m. The channel rate is 24 Mb/s and the bit stream includes synchronization and error detection mechanisms. The power consumption, approximately 142 mW, is low enough to allow the system to operate continuously for 33 h, using two 3.6-V/1200-mAh Li-SOCl2 batteries. The transmitter was designed using off-the-shelf components and is assembled in a stack of three 28 mm ? 28-mm boards that fit in a 38 mm ? 38 mm ? 51-mm aluminum enclosure, a significant size reduction over the initial version of HermesD. A 7-dBi circularly polarized patch antenna is used as the transmitter antenna, while on the receiver side, a 13-dBi circular horn antenna is employed. The advantages of using circularly polarized waves are analyzed and confirmed by indoor measurements. The receiver is a stand-alone device composed of several submodules and is interfaced to a computer for data acquisition and processing. It is based on the superheterodyne architecture and includes automatic frequency control that keeps it optimally tuned to the transmitter frequency. The HermesD communications performance is shown through bit-error rate measurements and eye-diagram plots. The sensitivity of the receiver is -83 dBm for a bit-error probability of 10(-9). Experimental recordings from a rhesus monkey conducting multiple tasks show a signal quality comparable to commercial acquisition systems, both in the low-frequency (local field potentials) and upper-frequency bands (action potentials) of the neural signals. This system can be easily scaled up in terms of the number of channels and data rate to accommodate future generations of Hermes systems.

HermesC: low-power wireless neural recording system for freely moving primates

Neural prosthetic systems have the potential to restore lost functionality to amputees or patients suffering from neurological injury or disease. Current systems have primarily been designed for immobile patients, such as tetraplegics functioning in a rather static, carefully tailored environment. However, an active patient such as amputee in a normal dynamic, everyday environment may be quite different in terms of the neural control of movement. In order to study motor control in a more unconstrained natural setting, we seek to develop an animal model of freely moving humans. Therefore, we have developed and tested HermesC-INI3, a system for recording and wirelessly transmitting neural data from electrode arrays implanted in rhesus macaques who are freely moving. This system is based on the integrated neural interface (INI3) microchip which amplifies, digitizes, and transmits neural data across a approximately 900 MHz wireless channel. The wireless transmission has a range of approximately 4 m in free space. All together this device consumes 15.8 mA and 63.2 mW. On a single 2 A-hr battery pack, this device runs contiguously for approximately six days. The smaller size and power consumption of the custom IC allows for a smaller package (51 x 38 x 38 mm (3)) than previous primate systems. The HermesC-INI3 system was used to record and telemeter one channel of broadband neural data at 15.7 kSps from a monkey performing routine daily activities in the home cage.

Chronic multi-electrode neural recording in free-roaming monkeys

Many behaviors of interest to neurophysiologists are difficult to study under laboratory conditions because such behaviors are often inhibited when an animal is restrained and socially isolated. Even under the best conditions, such behaviors may be sparse enough as to require long duration neural recordings or simultaneous recording of multiple neurons to gather a sufficient amount of data for analysis. We have developed a preparation for chronic, multi-electrode recordings in the auditory cortex of marmoset monkeys, small primates, as well as techniques for neurophysiological recordings when the animals are free-roaming while singly caged in the environment of the monkey colony. In this report, we describe our solutions to overcome the problems associated with chronic recordings in free-roaming animals, where three-dimensional movements present particular challenges.

On the role of the pontine brainstem in vocal pattern generation: a telemetric single-unit recording study in the squirrel monkey

In a recent study, we localized a discrete area in the ventrolateral pontine brainstem of squirrel monkeys, which seems to play a role in vocal pattern generation of frequency-modulated vocalizations. The present study compares the neuronal activity of this area with that of three motoneuron pools involved in phonation, namely the trigeminal motor nucleus, facial nucleus, and nucleus ambiguous. The experiments were performed in freely moving squirrel monkeys (Saimiri sciureus) during spontaneous vocal communication, using a telemetric single-unit recording technique. We found vocalization-related activity in all motoneuron pools recorded. Each of them, however, showed a specific profile of activity properties with respect to call types uttered, syllable structure, and pre-onset time. Different activity profiles were also found for neurons showing purely vocalization-correlated activity, vocalization- and mastication-correlated activity, and vocalization- and respiration-correlated activity. By comparing the activity properties of the proposed vocal pattern generator with the three motoneuron pools, we show that the pontine vocalization area is, in fact, able to control each of the three motoneuron pools during frequency-modulated vocalizations. The present study thus supports the existence of a vocal pattern generator for frequency-modulated call types in the ventrolateral pontine brainstem.

Audio-vocal interaction in the pontine brainstem during self-initiated vocalization in the squirrel monkey

The adjustment of the voice by auditory input happens at several brain levels. The caudal pontine brainstem, though rarely investigated, is one candidate area for such audio-vocal integration. We recorded neuronal activity in this area in awake, behaving squirrel monkeys (Saimiri sciureus) during vocal communication, using telemetric single-unit recording techniques. We found audio-vocal neurons at locations not described before, namely in the periolivary region of the superior olivary complex and the adjacent pontine reticular formation. They showed various responses to external sounds (noise bursts) and activity increases (excitation) or decreases (inhibition) to self-produced vocalizations, starting prior to vocal onset and continuing through vocalizations. In most of them, the responses to noise bursts and self-produced vocalizations were similar, with the only difference that neuronal activity started prior to vocal onset. About one-third responded phasically to noise bursts, independent of whether they increased or decreased their activity to vocalization. The activity of most audio-vocal neurons correlated with basic acoustic features of the vocalization, such as call duration and/or syllable structure. Auditory neurons near audio-vocal neurons showed significantly more frequent phasic response patterns than those in areas without audio-vocal activity. Based on these findings, we propose that audio-vocal neurons showing similar activity to external acoustical stimuli and vocalization play a role in olivocochlear regulation. Specifically, audio-vocal neurons with a phasic response to external auditory stimuli are candidates for the mediation of basal audio-vocal reflexes such as the Lombard reflex. Thus, our findings suggest that complex audio-vocal integration mechanisms exist in the ventrolateral pontine brainstem.

Localization of a vocal pattern generator in the pontine brainstem of the squirrel monkey

Very little is known about the coordination of muscles involved in mammalian vocalization at the level of single neurons. In the present study, a telemetric single-unit recording technique was used to explore the ventrolateral pontine brainstem for vocalization-correlated activity in the squirrel monkey during vocal communication. We found a discrete area in the reticular formation just above the superior olivary complex showing vocalization-correlated activity. These neurons showed an increase in neuronal activity exclusively just before and during vocalization; none of them was active during mastication, swallowing or quiet respiration. Furthermore, the neuronal activity of these neurons reflected acoustic features, such as call duration or syllable structure of frequency-modulated vocalization, directly. Based on these findings and previously reported anatomical data, we propose that this area serves as a vocal pattern generator for frequency-modulated call types.