NeuroNexus · neuronexus.com · Glossary
Spectral Analysis (Spectrogram and Coherence)
Spectral analysis describes a field potential by frequency: a power spectrum gives the power in each band, a spectrogram shows how that power changes over time, and coherence measures how strongly two signals are correlated at each frequency, from 0 to 1.
The conventional bands are delta (1 to 4 Hz), theta (4 to 8), alpha (8 to 13), beta (13 to 30) and gamma (above 30), and a spectrogram's window length, typically 50 to 500 ms, sets its time resolution against its frequency resolution. Coherence is the cross-spectrum divided by the two auto-spectra and needs trial averaging to be reliable.
What the electrode changes is what a channel's spectrum means. Power is summed over the tissue a site averages, so a large site or a surface grid gives a cleaner, more regional spectrum and a small site a more local one; and a distant reference adds the reference's own rhythms to every channel, so coherence between two channels that share a reference can be the reference rather than the brain. Bregma-aligned grids, fixed session structure and staging from an independent signal are what make spectral and coherence differences comparable across animals, as the rat EEG study shows. Spectrograms are interactive in Radiens Videre.
Typical values
| Bands | delta 1–4 · theta 4–8 · alpha 8–13 · beta 13–30 · gamma > 30 Hz |
|---|---|
| Spectrogram window, typical | 50 to 500 ms |
| Coherence | 0 (none) to 1 (perfect), per frequency |
Related Terms
Cite this term
NeuroNexus. "Spectral Analysis (Spectrogram and Coherence)." NeuroNexus Glossary, updated 2026-10-12. https://www.neuronexus.com/resources/glossary/spectral-analysis