# Brain-Inspired Healthcare Smart System Based on Perception-Action Cycle
## 3 Electroencephalography  
Electroencephalography (EEG) studies, compared to other imaging techniques or behavioral observations, have advantages because of their excellent time resolution since several records can be taken in a second through multiple sensors. For example, magnetoencephalography (MEG) records the electric field activity generated by neurons and has excellent resolution in time, but it requires large, stationary and expensive detectors. On the other hand, the change in blood flow associated with neuronal activity is measured by Functional Magnetic Resonance Imaging (fMRI), since oxygenated blood compared to the rest causes magnetic distortions that are generated by the protons present in it, so fMRI has excellent spatial resolution [8]. Since human neuronal activity has a high degree of complexity in its nature, neuronal oscillations can be measured as a mixture of several underlying base frequencies, which reflect certain cognitive, attentive and affective states. These oscillations were defined in specific frequency-ranges such as gamma (\(\gamma\), +25 Hz), beta (\(\beta\), 12-25 Hz), alpha (\(\alpha\), 8-12 Hz), theta (\(\theta\), 4-8 Hz), and delta (\(\delta\), 1-4 Hz) [8; 9; 10], Figure 3.  
* Delta (1-4 Hz): These types of waves have been examined during periods of deep sleep, locating their point of greatest power in the right hemisphere of the brain. Since sleep is associated with memory consolidation, it plays a central role in learning functions. Its amplitude varies from 20-200 \(\upmu\)V.
* Theta (4-8 Hz): Some studies report that the activity of this wave is related to cognitive activities such as selective attention, assimilation of information, processing, learning and working memory. Anyone can have a better record from the prefrontal, central, parietal and temporal areas. Its amplitude varies from 20-100 \(\upmu\)V.
* Alpha (8-12 Hz): This rhythmic oscillatory activity is involved when there is a response to sensory stimuli, motor functions and memory. High levels of alpha can be noted when there is relaxation with closed eyes, the suppression of alpha implies a characteristic signature of mental states of interest, e.g., when there is sustained attention to any type of stimulus at a particular time. Its amplitude varies from 20-60 \(\upmu\)V and the source of activation of these signals is in the occipital region of the brain. * Beta (12-25 Hz): This frequency is generated both in the occipital and frontal regions, the states of active thinking, motor functions, visual and spatial coordination, anxiety and concentration are associated. Its amplitude varies from 2-20 \(\upmu\)V.
* Gamma (more than 25 Hz): They usually have the highest frequency and the lowest amplitude. So far there is no strong association of what these types of waves reflect in the brain, there are some researchers who suggest being the reflection of the interconnection of several sensory responses to an object in a coherent way, therefore, it would represent a process of attention due to intense brain activities. On the other hand, others think that it is the effect of neuronal processes to achieve vision control, and, therefore, would not represent a cognitive process after all. There is discussion to date about a sixth cerebral rhythm called \(\mu\), its frequency band covers practically the same as alpha, however, it is only observed in the sensory-motor cortex [11]. These types of signals need to be discretized, which is why it is also important to define that signal processing consists of the representation, transformation and manipulation of signals in general, e.g., in their numerical representations of finite precision sequences. Typically, these systems work in real time, which means that a discrete system speeds processing; its applications include, among others, control systems, communications, radar, sonar, coding and voice and video enhancement, or biomedical engineering. Figure 4 shows the way the EEG sensor records the human brain activity (RAW sample).