Use of Telemetric EEG in Brain Injury

Telemetry technology allows remote measurement and recording of signals such as biopotentials. This technology offers the advantage of long-term EEG recordings without causing unnecessary distress, as happens in EEG systems where implanted leads connect to the recording device through a cable. The EEG recordings can be used to detect changes in the brain activity after a traumatic event. The use of telemetry for EEG acquisition is the most reliable option in experimental studies due to the reduction of animal stress. Besides its current disadvantages, such as a reduced number of channels when compared to tethered EEG, telemetry can allow us to distinguish oscillatory brain patterns that become pathological after a neurological injury. Normal brain oscillatory synchronization can be correlated with cognitive function and behavioral state. However, abnormal brain oscillations can be caused by pathologies characterized by dysfunction of the cholinergic system and trauma, leading to epilepsy. This phenomenon is the result of abnormal hypersynchronous firing in certain neuronal populations in the brain. Although not all kinds of brain injury can induce epilepsy, the spike/wave activity present during epileptic seizures is of special relevance, because severe brain injury can, in most cases, induce epilepsy. The combination of EEG acquired through telemetry and video is widely used for assessment of epileptic focus, to distinguish epileptic seizures from psychogenic non-epileptic seizures, reassessment for potential surgery to treat epilepsy and to study animal models. Nevertheless, the assessment of the long-term EEG changes that occur after brain injury is a challenge, because a large amount of data is accumulated. Reducing the sampling rate and/or the recording schedule is not an option since each subject may respond differently to the injury and treatment. Furthermore, seizure-like events do not occur in pre-determined periods, therefore arbitrary sampling would compromise acquisition and analysis. In order to acquire reliable results, one requires a good estimation of duration and frequency of seizures and/or the duration of sleep stages. Several studies have addressed the need for analytical tools capable of optimally performing spectral analyses and, in this chapter, we evaluate the advantages and disadvantages of some available tools. The reduction and removal of artifacts in the acquired data, spectral decomposition of the signal using fast Fourier and wavelet transforms, and batch-processing will also be discussed. We will provide a view of the role of telemetric EEG technology in neuroscience, focusing on the study of brain injury induced by chemical means. Approaches to assess long-term EEG changes, choices of acquisition parameters, and tools to analyze the EEG data will be introduced.