Recording neural data using Deuteron’s neural loggers
An introduction.
Deuteron Technologies makes a variety of neural recording devices primarily intended as research tools that allow the recording of neural signals on small, freely moving animals without the need for wired tethers.
Deuteron’s loggers are not limited to recording of neural signals; some of them also provide audio (or ultrasonic) recording and recording of the animal’s motion. Some systems can also provide electrical stimuli to the animal.
The loggers are presently used on a wide variety of animals, including:
- Rodents: Rats and mice
- Primates: Marmosets and macaques
- Bats:
- Fish: Archer fish and carp (goldfish)
- Birds: Pigeons and barn owls
- Non-animals:
- Humans: Limited to electrodes mounted on the skin
- Tissue cultures in incubators.
Most commonly, the loggers are used to record spikes from individual neurons from extra-cellular micro-electrodes, so they typically have a bandwidth of about 7kHz and a sampling rate of 30-32 kilo-samples per second. Some loggers are also able to record at lower bandwidths, typically sampling at 4ks/s for use with LFP, EEG and EMG studies.
Deuteron’s neural loggers are presently available capable of recording from 8,16,32,64 or 128 electrodes. Higher capacities will be available in the future.
The most basic function of a neural logger is to record large volumes of neural signals onto an animal-borne memory card that can later be taken and analyzed. Loggers can also send limited samples of the neural data wirelessly to a host computer to allow the user to pre-view the signals before beginning a measurement session.
The loggers are designed to connect to electrodes implanted in an animal via a connector. Deuteron does not presently supply electrodes or electrode drive assemblies, so researchers will need to obtain these from other suppliers and implant them before a logger can be used. Loggers are available with the most common connectors from Omnetics Mill-Max, Hirose and Molex. For other connectors, adapters can be provided. Alternatively, when Deuteron’s modular loggers are used, a custom preamplifier board can be provided.
There are many clear advantages of making neural recordings on untethered animals. Animals can be free to move in all directions, allowing motion in 3D mazes, swimming, flight, and ease of conduct of experiments involving multiple animals. These loggers also facilitate neural recording in unusually large arenas. The standard radio range of a Deuteron logger is about 20 meters, though some loggers have long-range radio allowing arenas for flying animals to extend to several hundred meters. An alternative to on-animal data recording is radio telemetry, where the neural signals are sent continuously by radio to a computer. Deuteron does not presently provide radio telemetry systems.
When making wireless neural recordings there are four obvious issues that need attention that do not exist with tethered systems, namely, on-animal data storage, battery power, synchronization and real-time data access. Each of these has been addressed in the design of Deuteron’s neural logging systems, as follows
Data Storage: The logger must have enough data storage space to record all the required neural data. MicroSD memory cards that weigh just 0.25g are used in almost all of Deuteron’s loggers, and these presently have capacities of up to 1.0TB. In almost all cases, this is much more than is needed. For example, when recording 64 channels at 32 kilosamples per second per channel, a 128GB card provides storage for 8 hours of continuous data.
Battery power: The animal must carry the power source for the data logger, which is generally a rechargeable battery. Deuteron’s loggers have been engineered to use very little power, roughly one third of the power consumption of competitive loggers. A typical requirement is about one gram of battery for each hour of neural recording in a 64-channel system. For a fuller discussion of battery sizes and weight, see Battery Specifications.
Synchronization: In most experiments, neural data needs to be analyzed relative to the timing of events that affect the animal. Deuteron provides a wide variety of methods to synchronize the recorded data with other events in the lab. This starts with a proprietary method for keeping the clock of the logger perfectly synchronized with the other clocks in the system. About 8 methods are provided for synchronizing neural and lab events.
Real-time access to neural data: Wireless loggers, in general, cannot provide wireless access to all of the data being collected as it is collected. This is because a typical radio link can only convey a limited amount of data per unit time, and generally, this is much less than the amount of data being collected. For example, a typical “wideband” radio link could have a raw capacity of 1Mbit per second, and can convey about 100kBytes per second. A 64-channel logger collects 4Mbytes per second, about 40 times the capacity of the radio link. Deuteron’s loggers provide partial solutions to this. All neural loggers support “monitor mode” in which a subset of the data is streamed wirelessly and displayed or conveyed to user’s programs for further processing.
For some loggers, it is also possible to attach a cable and stream data over a tether in order to conduct initial measurements before allowing the animal to move freely.It is noteworthy that as the amount of data that is collected increases, it becomes increasingly impractical to process neural data in real time as it is collected, thus the usefulness of access to real-time data drops as the number of electrodes increases. Deuteron is interested to hear details of proposed experiments where real-time access to neural data is an absolute requirement, and researchers interested in conducting such experiments are encouraged to contact Deuteron to discuss such needs, so that future versions of loggers can be designed to provide a solution.