Electroencephalography (EEG) is a valuable tool for studying brain activity in individuals with psychiatric disorders. The EEG test records electrical activity in the brain and provides insights into the neurological functioning associated with conditions like schizophrenia and depression. Below, we explore the EEG findings in patients with these conditions, progressing from basic concepts to more advanced insights.

1. Basic Concepts of EEG

EEG is a technique used to measure the electrical activity of the brain. It uses small electrodes placed on the scalp to detect brainwave patterns. The brain's electrical activity is categorized into various waveforms, including:

  • Delta Waves (<0.5 - 4 Hz): Seen in deep sleep and coma.
  • Theta Waves (4 - 8 Hz): Common in light sleep, drowsiness, and some cognitive states.
  • Alpha Waves (8 - 12 Hz): Associated with relaxed, calm states and awake but resting brain activity.
  • Beta Waves (12 - 30 Hz): Associated with active thinking, focus, and problem-solving.
  • Gamma Waves (>30 Hz): Linked to higher mental activity such as attention and memory.

2. EEG in Schizophrenia

Schizophrenia is a complex psychiatric disorder characterized by hallucinations, delusions, cognitive dysfunction, and altered perception of reality. EEG findings in schizophrenia can vary, but research indicates some common abnormalities:

  • Abnormal Alpha Activity: Reduced or altered alpha wave activity is often observed in schizophrenia. Studies show a decrease in the typical 8-12 Hz alpha rhythm, particularly in the posterior regions of the brain (e.g., occipital lobe). This abnormality may reflect impaired sensory processing and attentional deficits in patients.
  • Increased Theta and Delta Waves: Increased theta (4-8 Hz) and delta (<4 Hz) waves in the frontal regions are commonly seen in schizophrenia. These slow-wave activities are associated with cognitive impairments and may indicate dysfunctional brain regions responsible for attention, memory, and executive functions.
  • Reduced Alpha Connectivity: Studies have shown a reduction in connectivity between brain regions, particularly between the frontal and posterior areas. This could reflect impaired cognitive integration and the disorganization often seen in schizophrenia.
  • Increased Beta Activity: Elevated beta waves, especially in the frontal regions, have been noted in some patients, correlating with psychotic symptoms such as hallucinations and delusions.

3. EEG in Depression

Depression, particularly major depressive disorder (MDD), is marked by persistent feelings of sadness, loss of interest, and a range of cognitive and somatic symptoms. EEG findings in depression reflect alterations in brain activity related to mood regulation and cognitive processing:

  • Increased Theta Waves: Increased theta wave activity in the frontal regions is frequently observed in depression. This is often associated with impaired cognitive function and emotional regulation, and may contribute to the lethargy and poor concentration seen in depressive states.
  • Decreased Alpha Waves: A reduction in alpha activity, particularly in the posterior regions of the brain, has been linked to depression. This suggests altered attention and relaxation mechanisms, which can lead to the cognitive difficulties experienced by individuals with depression.
  • Frontal Asymmetry: Frontal asymmetry refers to the imbalance of brain wave activity between the left and right hemispheres. In depression, a characteristic finding is greater alpha or theta activity in the right frontal hemisphere compared to the left. This may indicate an overactivity of the right hemisphere, which is often associated with negative emotional states.
  • Slow Cortical Potentials: In depressed individuals, the presence of slow cortical potentials (low-frequency oscillations) has been reported. These may reflect an inability of the brain to properly regulate emotional states and might contribute to the feeling of “mental fog” often noted in depression.

4. Advanced Insights and Interpretation of EEG Findings

EEG is a non-invasive diagnostic tool, but its interpretation in psychiatric conditions such as schizophrenia and depression requires careful consideration of various factors:

  • EEG as a Biomarker: While EEG abnormalities in schizophrenia and depression are common, they are not specific to these conditions. Researchers are working on using EEG patterns as potential biomarkers to better diagnose and differentiate these disorders from other neurological and psychiatric conditions.
  • EEG and Treatment Response: Changes in EEG activity have been used to monitor the effects of treatments such as antidepressants or antipsychotics. For instance, normalization of abnormal theta activity in depression may indicate a positive response to treatment.
  • Connectivity and Network Analysis: Advanced methods, such as EEG coherence and network analysis, are being used to study the connectivity between different brain regions in schizophrenia and depression. Altered brain network connectivity may offer insights into the pathophysiology of these disorders and how they affect cognitive and emotional processes.

5. Conclusion

EEG findings in schizophrenia and depression provide valuable insights into the underlying neural abnormalities associated with these conditions. In schizophrenia, there is typically reduced alpha activity, increased theta/delta waves, and abnormal connectivity, reflecting cognitive dysfunction and psychosis. In depression, increased theta waves, decreased alpha activity, and frontal asymmetry are common, reflecting the cognitive and emotional disturbances associated with the disorder. EEG continues to be a powerful tool for understanding the pathophysiology of these psychiatric disorders and for guiding treatment monitoring.