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Monitoring Disease Activity in Multiple Sclerosis
Published in Richard K. Burt, Alberto M. Marmont, Stem Cell Therapy for Autoimmune Disease, 2019
Evoked potentials (EP) are electrical potentials that are induced by sensory stimuli. Scalp electrodes are used to record the potentials. When demyelination occurs in the central or peripheral nervous system, the potentials are delayed, decreased in size or absent. Evoked potentials have been used for the diagnosis of MS, particularly with clinically silent lesions. For example, “tingling” in the arms or legs without findings on the examination may be associated with abnormal somatosensory evoked potentials. Similarly, “blurred vision’ without a central scotoma or afferent pupillary defect may be indicative of optic neuritis, confirmed by visual evoked potentials. The most recent criteria for diagnosis of MS suggest visual evoked potentials are the only useful evoked potential for the confirmation of disease symptoms.44
Digital Biomedical Signal Acquisition and Processing
Published in Hualou Liang, Joseph D. Bronzino, Donald R. Peterson, Biosignal Processing, 2012
Luca T. Mainardi, Anna M. Bianchi, Sergio Cerutti
Traditional filtering performs very well when the frequency content of signal and noise do not overlap. When the noise bandwidth is completely separated from the signal bandwidth, the noise can be decreased easily by means of a linear filter according to the procedures described earlier. On the other hand, when the signal and noise bandwidth overlap and the noise amplitude is enough to seriously corrupt the signal, a traditional filter, designed to cancel the noise, also will introduce signal cancellation or, at least, distortion. As an example, let us consider the brain potentials evoked by a sensory stimulation (visual, acoustic, or somatosensory) generally called evoked potentials (EP). Such a response is very difficult to be determined because its amplitude is generally much lower than the background EEG activity. Both EP and EEG signals contain information in the same frequency range; thus, the problem of separating the desired response cannot be approached via traditional digital filtering (Aunon et al., 1981). Another typical example is in the detection of ventricular late potentials (VLP) in the ECG signal. These potentials are very small in amplitude and are comparable with the noise superimposed on the signal and also for what concerns the frequency content (Simson, 1981). In such cases, an increase in the SNR may be achieved on the basis of different statistical properties of signal and noise.
Protocol and Process of EEG Data Acquisition
Published in Narayan Panigrahi, Saraju P. Mohanty, Brain Computer Interface, 2022
Narayan Panigrahi, Saraju P. Mohanty
Evoked potentials are those components of the EEG that arise in response to a stimulus (which may be electric, auditory, visual, etc.). Such signals are usually below the noise level and thus not readily distinguished. One must use a train of stimuli to the subject and perform signal processing such as signal averaging to improve the signal-to-noise ratio before analysis of the evoke potential.
Developments in the human machine interface technologies and their applications: a review
Published in Journal of Medical Engineering & Technology, 2021
Harpreet Pal Singh, Parlad Kumar
Evoked signals: Evoked signals or evoked potentials are the electrical signals produced by the specific part of the nervous system, especially the brain, in response to an external stimulus. Some evoked signals are P300, auditory-visual potential (AVP), steady-state evoked potentials (SSEP) and visual events potential (VEP) or steady-state visual event potential (SSVEP) [45]. P300 gives peak amplitude at approximately 300 ms after ensuing visual or auditory stimulus. AVP signals are produced at the cortex portion after the effect of sound frequencies impinging on it and results in generating the potential difference of the same frequency. VEP or SSVEP are generated due to visually evoked potential, ensued from the visual stimulus and detected at cerebral cortex portion [46].
TeleBCI: remote user training, monitoring, and communication with an evoked-potential brain-computer interface
Published in Brain-Computer Interfaces, 2020
Andrew Geronimo, Zachary Simmons
BCI technologies in particular offer the possibility of eye-independent communication through the user’s intentional modulation of brain activity. An early demonstration of this featured the self-regulation of slow cortical potentials to translate thoughts into “yes’ and ‘no’ commands [7]. Since that time, one of the most widely implemented BCI control signals is the ‘oddball’ paradigm, where a target stimulus is presented infrequently and randomly within a larger group of non-target stimuli. By responding to the presentation of only target stimuli by, in the case of this study, counting the target stimuli as they appear, a target-specific evoked potential (EP) can be measured at the scalp. The P300 is a positive component of this EP, generally the most prominent feature of the oddball evoked response, originating at the centro-parietal midline with latency of approximately 300 milliseconds [8]. Other components such as the N170 and N400f are elicited during the process of face recognition [9], the use of which has recently been employed for BCI use [10,11]. The ‘P300 speller’ is a BCI paradigm that makes typing selections based on the evoked responses to a target stimulus.