Abstract
Alpha event-related desynchronization (ERD) has been widely applied to understand the psychophysiological role of this band in cognition. In particular, a considerable number of publications have described spectral alterations in several pathologies using this time-frequency approach. However, ERD is not capable of specifically showing nonphase (induced) activity related to the presentation of stimuli. Recent studies have described an evoked and induced activity in the early phases (first 200 ms) of stimulus processing. However, scarce studies have analyzed induced and evoked modulations in longer latencies (>200 ms) and their potential roles in cognitive processing. The main goal of the present study was to analyze diverse evoked and induced modulations in response to visual stimuli. Thus, 58-channel electroencephalogram (EEG) was recorded in 21 healthy subjects during the performance of a visual attention task, and analyses were performed for both target and standard stimuli. The initial result showed that phase-locked and nonphase locked activities coexist in the early processing of target and standard stimuli as has been reported by previous studies. However, more modulations were evident in longer latencies in both evoked and induced activities. Correlation analyses suggest that similar maps were present for evoked and induced activities at different timepoints. In the discussion section, diverse proposals will be stated to define the potential roles of these modulations in the information processing for this cognitive task. As a general conclusion, induced activity enables the observation of cognitive mechanisms that are not visible by ERD or ERP modulations.
Highlights
Diverse domains have been studied in the electroencephalographic response during cognitive tasks, including a time domain (event-related potentials (ERPs)) and a frequency domain, among other domains [1]
Evoked and induced alpha modulations alpha, beta, and theta) in multiple cognitive paradigms [2, 3, 4]. One of these techniques was defined as event-related desynchronization (ERD) [5, 6]. When it was first developed, alpha ERD was interpreted as a decrement of the synchrony of the alpha band; a reduction would mean an activation of the neural tissue
In the low alpha (8–10.5 Hz), a double interaction between the “TYPE” of stimuli and “ACTIVITY” factors was significant (F(1,20 = 10.02, p = 0.004) (η2 = 0.334) for the latency parameter. This effect was caused by a faster latency of the induced activity (120 ± 36.2 ms) in the target stimuli than that of the evoked activity (135 ± 40.3 ms) (p = 0.038), which did not occur in the case of the standard stimuli
Summary
Diverse domains have been studied in the electroencephalographic response during cognitive tasks, including a time domain (event-related potentials (ERPs)) and a frequency domain, among other domains [1]. One of these techniques was defined as event-related desynchronization (ERD) [5, 6] When it was first developed, alpha ERD was interpreted as a decrement of the synchrony of the alpha band (assuming alpha oscillation as an idling status for neural networks); a reduction would mean an activation of the neural tissue. Another option described at the beginning of this technical approach was the event-related synchronization (ERS). This concept was intended to represent, in the case of the alpha band, a higher synchronized activity for this frequency and a relaxation of the neural structures involved [7]
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