Journal of Neuroscience Methods 201 (2011) 106–115 Contents lists available at ScienceDirect Journal of Neuroscience Methods j o ur nal homep age: www.elsevier.com/locate/jneumeth A novel telemetry system for recording EEG in small animals Pishan Chang a,1 , Kevan S. Hashemi b,∗ , Matthew C. Walker a a Department of Clinical and Experimental Epilepsy, UCL Institute of Neurology, University College London, London WC1N 3BG, United Kingdom b OpenSource Instruments Inc., Watertown, MA 02472, United States a r t i c l e i n f o Article history: Received 22 December 2010 Received in revised form 14 July 2011 Accepted 19 July 2011 Keywords: Electroencephalography Epilepsy Wireless telemetry Rats Open source a b s t r a c t It has become increasingly evident that continuous EEG monitoring is necessary to observe the develop- ment of epilepsy in animals, and to determine the effect of drugs on spontaneous seizures. Telemetric recording systems have been increasingly used to monitor EEG in freely moving animals. One challenge faced by such systems is to monitor frequencies above 80 Hz continuously for weeks. We present an implantable, 2.4-ml, telemetric sensor that can monitor EEG at 512 samples per second for eight weeks in a freely moving animal. With minor modifications, the same transmitter can operate at higher sample rates with a proportional decrease in operating life. Signal transmission is through bursts of 915-MHz radio power. The burst transmission and several other novel techniques reduce the transmitter’s power consumption by two orders of magnitude while allowing 8 transmitters to share the same recording system. The use of radio-frequency transmission permits digitization within the sensor to sixteen-bit resolution, thus eliminating transmission-generated signal noise. The result is a signal with dynamic range 9 mV, bandwidth 160 Hz, input noise 12 V, and AC power interference less than 1 V. All circuit diagrams are open-source. Data acquisition takes place over the Internet using open-source software that works on multiple operating systems. The resulting system permits long-term, continuous, monitoring of EEG signals, therefore providing continuous and reliable data upon which to base studies of epilepsy in freely moving animals. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Epilepsy is the propensity to have spontaneous seizures. Seizures are transient symptoms associated with abnormal, exces- sive, or synchronous neuronal activity in the brain. They can cause a variety of temporary and debilitating changes in perception and behavior. Epilepsy is one of the most common serious neuro- logical diseases, affecting 0.5–1% of the population (Sander and Shorvon, 1996). The drugs that we presently use to treat epilepsy are symptomatic; they prevent seizures rather than modify the condition. Furthermore, these drugs treat only 70% of people suc- cessfully (Kwan and Brodie, 2000). More effective treatments and disease-modifying treatments are urgently needed (Walker et al., 2002). Acquired and genetic animal models of spontaneous seizures have been developed to investigate the mechanisms underlying the development of epilepsy (epileptogenesis) and to evaluate Abbreviations: SE, status epilepticus; EEG, electroencephalogram; LWDAQ, long- wire data acquisition driver; SCT, subcutaneous transmitter. ∗ Corresponding author. Tel.: +1 781 736 2819. E-mail address: hashemi@opensourceinstruments.com (K.S. Hashemi). 1 Present address: Centre for Biomedical Sciences, School of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, United Kingdom. the effect of drugs on epileptogenesis and spontaneous seizures (Schmidt and Rogawski, 2002). It has become increasingly appar- ent that continuous electroencephalogram (EEG) is required to observe the effects of treatment and for mapping the development of epilepsy (Williams et al., 2009), especially because ictal EEG activity can precede the earliest observable changes in behavior (Lieb et al., 1976; Litt et al., 2001). Monitoring physiological signals in a rodent can be achieved by running wires from the animal’s body to amplifiers and recording equipment outside the cage. Such “tethered systems” have been successful in long-term monitoring of EEG and have permitted the correlation of EEG with behavior. Unlike battery-operated systems, tethered systems can provide the power necessary for long-term recordings with multiple electrodes and high sampling rate. There are, however, several disadvantages to tethered systems. Being tethered by wires can cause some distress to the animals, a potential source of experimental artifact and inter-animal variabil- ity (Kramer et al., 2001). Whenever the animal moves, the tethering wires also move. These movements interact with electrostatic fields in the animal’s cage, resulting in transient noise known as “move- ment artifact”. This noise can be difficult to differentiate from biological signals. Moreover, any separation between the wires causes them to detect magnetic fields generated by nearby alter- nating currents, resulting in 50-Hz or 60-Hz noise termed “mains 0165-0270/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jneumeth.2011.07.018