If we assume that each cortical network has its own characteristic temporal dynamics which is apparent in the EEG trace, then the dimension estimates the number of independently active cell assemblies, i.e the cortical complexity, for a given mental, motor or sensory activity. Table 1 gives examples of EEG-complexity, which is a monotonous function of the number of independent cell assemblies of the EEG during different activities. Each cell represents the result of one experiment.
| States of consciousness | |
| coma (apallic syndrome) | decreased compared to wakefulness |
| anesthesia (with sedatives) | reduced compared to wakefulness and dreaming (REM) |
| sleep | markedly reduced during deep (slow wave) sleep compared to wakefulness and dreaming (REM) |
| menstrual cycle | no differences during different phases of the cycle |
| Development, Aging and Personality | |
| 7 years up to 50 years | monotonous increase with age intelligence, increased in intelligent persons when no stimulus presented,no difference during stimulus presentation or task performance |
| musically sophisticated versus untalented subjects | markedly reduced during regular rhythmical music in subjects preferring simple ("pop") music |
| Perception | |
| eyes closed | no difference to eyes open imagery, always increased during imagination of objects, sounds or temperature compared to real perception of the same objects |
| observing double versus simple pendulum increased with double figures music | increased with more unpredictable (complex) music |
| Cognitive processes | |
| focused attention | reduced compared to imagery and rest attentiveness |
| reduced during diffuse-passive stimulus anticipation compared to task preparation concentration | |
| during distraction increased divergent thinking | |
| ("creativity") | slightly increased compared to convergent thinking |
| mental rotation | during simple rotation higher than during complex rotation |
| stroop-test | reduced compared to rest, no interference effects |
| Motor process | |
| relaxation exercises | no difference to rest |
| deep breathing (hyperventilation) | no difference to rest |
| tapping | local increase over hand areas (C3 and C4) fine motor task (Luria), increased complexity with fine motor compared to tapping task |
| Emotional processes | |
| positive feelings | increased compared to negative feelings during rest condition |
| love | pronouncedly reduced in persons in love compared to persons not in love, no difference during mental activity |
| pain | reduced during thermic pain compared to control condition (only in pain insensitive persons) |
| Pathology and pharmaca | |
| smoking | reduced in smokers after smoking |
| Clonazepam (antiepileptic) | increased compared to placebo |
| Carbamazepin (antiepileptic) | no change compared to placebo |
| Parkinson½s disease | increased during performance and during imagination of complex motor tasks |
| schizophrenia | markedly increased in frontal lobe, reduced parietal lobe |
| chronic pain | increased during imagined pain in pain patients and pain sensitive persons compared to rest condition and healthy persons |
| tinnitus (noise in the ear) | increased compared to healthy persons |
The estimate of the number of simultaneously active cell assemblies contains no information about the functional meaning of the activity of a given assembly. Mental activity is represented in Hebbian cell assemblies which oscillate proportional to their anatomical size and connections within the cerebral cortex. These oscillations are frequently called gamma-band or 40Hz oscillations because they can be found only in the high-frequency beta range. From animal experiments it is concluded that synchronous high frequency activity indicates Hebbian strengthening of cell assemblies ("binding") necessary to represent meaning and Gestalt in the nervous system. Each mental act is represented in a topographically different assembly which has in a specific frequency of oscillation. If these oscillations represent the construction of meaning, Gestalt or context in the nervous system, they should appear whenever humans find meaning in a formally meaningless pattern. This was confirmed for the visual modality and for language (see Neurobiology of Language
Birbaumer, N., Flor, H., Lutzenberger, W. & Elbert, T. (1994). Chaos and order in the human brain. In G. Karmos & M. Molnar (Eds): Perspectives of Event Related Potentials Research. EEG Suppl. 44, 448-457, Amsterdam: Elsevier.
Elbert, T., Ray, W.J., Kowalik, Z.J., Skinner, J.E., Graf, K.E. & Birbaumer, N. (1994). Chaos and Physiology: Deterministic Chaos in Excitable Cell Assemblies. Physiological Reviews, 74, 1, 1 - 4787. Lutzenberger,W., Pulvermüller, F., Elbert,T. & Birbaumer, N. (1995). Visual stimulation alters local 40-Hz responses in humans: an EEG study. Neuroscience Letters 183, 1-4.
Schupp, H.T., Lutzenberger, W., Birbaumer, N., Miltner, W. & Braun, C. (1994). Neurophysiological differences between perception and imagery. Cognitive Brain Research 2, 77-86.