Electroencephalography (EEG) has gained importance in the objective study of mental and neurological states due to its high temporal resolution, noninvasiveness, and low cost. The increasing prevalence of neurological and mental health problems calls for reliable, data-driven diagnostic and monitoring techniques that go beyond traditional subjective assessments. This review provides a systematic overview of EEG-based mental state detection techniques, including data collection methods, preprocessing techniques, feature extraction strategies, and classification models. In order to capture discriminative patterns of brain activity across time, frequency, time–frequency, nonlinear, and connection domains, the significance of feature extraction techniques is examined. We cover both sophisticated deep learning architectures like Convolutional Neural Networks, Recurrent Neural Networks, and hybrid models, as well as fundamental machine learning classifiers like Random Forests and Support Vector Machines. According to published performance evaluations, deep learning-based techniques usually provide better resilience and classification accuracy. Despite these advancements, there are still significant issues with noise artifacts, inter-subject variability, the lack of datasets, and overlapping mental state characteristics. This review also outlines future research directions with a focus on improved preprocessing, improved feature learning, scalable model architectures, and therapeutically useful EEG-based systems.
Introduction
Electroencephalography (EEG) is a non-invasive technique for monitoring brain activity, useful for understanding mental states, neurological conditions (e.g., epilepsy, Parkinson’s, Alzheimer’s), and psychiatric disorders, as well as for brain-computer interfaces (BCIs). EEG signals are complex, noisy, and nonstationary, so feature extraction—including time-domain, frequency-domain, nonlinear, time-frequency, connectivity, and learned deep features—is crucial for meaningful analysis. Machine learning and deep learning techniques such as SVM, Random Forest, k-NN, CNNs, RNNs, LSTMs, and hybrid models are employed to classify EEG signals, enabling accurate detection of cognitive and emotional states. Advances in preprocessing, feature engineering, and deep learning have improved EEG classification, providing potential for more reliable mental health diagnosis, personalized care, and enhanced human-computer interaction.
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