People can measure scalp electric-voltage waves {electroencephalography}| (EEG).
cause
EEG wave voltages are sums of graded potentials in dendritic trees and their synapses [Creutzfeldt and Houchin, 1984] [Creutzfeldt, 1995] [Freeman, 1975] [Mountcastle, 1957] [Mountcastle, 1998] [Remond, 1984].
EEG potential changes are larger than neuron induced activity. Potential differences between cell bodies and neuron fibers influence EEG waves. Brain potential waves imply synchronized neuron activities, over distances more than two millimeters apart. Waves are coherent, not harmonic, across different cortical areas.
location
Electric waves appear in parietal lobe, then primary motor cortex and occipital lobe, and then prefrontal lobe.
amplitude
EEG wave voltages are 1 mV to 2 mV. To detect voltage change requires averaging hundreds of measurements to subtract noise. EEG can measure scalp potential differences less than 100 microvolts [Makeig et al., 2002].
correlations
Scalp evoked-potential changes in response to image, sound, or mental event [Galambos et al., 1981].
Anesthesia and responses to simple stimulus configurations can have prolonged brain potential synchronization. Brain-potential synchronization is less during awake states and complex situations.
Waves are large in tasks requiring activity integration across different cortical areas. Waves stop at perceptual-processing conclusion and motor-signaling beginning.
Waves do not carry information about stimuli nor relate to signals from individual neurons.
correlations: awake
Hippocampus has theta rhythm at 4 Hz to 10 Hz during active movement and alert immobility, synchronized between hemispheres and 8 mm along hippocampus longitudinal axis. Awake brain has synchrony, which increases with attention and preparation for motor acts. Brain potential synchronization is less when awake.
Other behaviors have local and bilaterally synchronous rhythm near 40 Hz.
200-Hz waves correlate with alert immobility.
A 12-millisecond phase shift goes from brain rostral to caudal pole, during alpha wave activity while awake.
Most waves during waking are in posterior cortex, lower than vertex.
correlations: sleep
EEG waves can differentiate seven sleep stages. Most waves during sleeping are in vertex and frontal lobe. Synchronous firing characterizes deep sleep and epilepsy.
Between waking and sleeping, brain wave change is abrupt in adults. Between waking and sleeping, brain wave change is slow in children.
correlations: slow-wave sleep
NREM sleep has low-frequency, high-amplitude waves. Non-REM-sleep phases 3 and 4 have low-frequency EEG waves {slow-wave sleep}.
correlations: REM sleep
Awake and REM sleep activation level has high-frequency, low-amplitude waves [Hobson, 1989] [Hobson, 1994] [Hobson, 1999] [Hobson, 1999] [Hobson, 2002] [Hobson et al., 1998].
correlations: other waves
EEG waves include bereitschaftspotential, contingent negative variation (CNV), and motor potential.
factors: age
EEG-wave localization, regularity, continuity, similarity from both hemispheres, synchrony from similar areas, and stability increase until age 35. Brain-wave amplitude decreases until age 35.
Alpha waves disappear when eyes open or people have mental imagery {alpha blocking}, but some visual activities do not block alpha waves. If both visual hemispheres have damage, alpha rhythm stops.
EEG waves {alpha wave} can have frequency range 8 to 12 per second. Sleep or quiet rest has alpha waves. They have larger amplitude if brain has pathology. A 12-millisecond phase shift goes from brain rostral to caudal pole, during alpha wave activity while awake and during REM sleep [Varela et al., 2001]. Alpha-wave frequency increases until five or six years old.
Electric potentials {auditory evoked potential} (AEP) happen after sounds [Creutzfeldt and Houchin, 1984] [Creutzfeldt, 1995] [Freeman, 1975] [Mountcastle, 1957] [Mountcastle, 1998] [Remond, 1984]. Scalp electrodes can record them.
sleep
AEP during waking and REM sleep are similar but differ from AEP during non-REM sleep. Early AEP do not fluctuate during sleep-waking cycle. Early thalamocortical activity causes middle AEP, which decrease amplitude from waking to stage-4 sleep but are normal in REM sleep.
Later, AEP amplitudes decrease from waking to stage-4 sleep but increase in REM sleep. P20 component reflects cerebral-cortex activity and increases from waking to stage-4 sleep but returns to waking level in REM sleep. REM sleep does not have latest AEP: P100 wave, P200 wave, and P300 wave.
EEG waves {beta wave} can have frequency range 15 Hz to 25 Hz. Beta-wave frequency increases until 15 years old.
EEG {bispectral index} can measure anesthesia depth.
EEG waves {delta wave} can have frequency range 1 Hz to 4 Hz. If sound is during REM-sleep delta-wave activity, no coherent 40-Hz oscillations begin [Creutzfeldt and Houchin, 1984] [Creutzfeldt, 1995] [Freeman, 1975] [Mountcastle, 1957] [Mountcastle, 1998] [Remond, 1984]. Delta-wave frequency increases until one year old.
Scalp potential {evoked potential} {event-related potential} changes in response to image, sound, or mental event [Galambos et al., 1981].
Concentrating on probable signal arrival changes electroencephalograph potential {expectancy wave} (e-wave).
Awake but non-attentive animals have large-amplitude synchronized 25-Hz to 35-Hz oscillations {gamma wave} [Engel and Singer, 2001] [Keil et al., 1999] [Klemm et al., 2000] [Revonsuo et al., 1997] [Rodriguez et al., 1999] [Tallon-Baudry and Bertrand, 1999].
locations
Visual precentral and postcentral cortex, retina, olfactory bulb, thalamus, other brain nuclei, and cerebral neocortex have continuous and coherent 30-Hz to 70-Hz {40-Hz oscillation} electric potential oscillations.
All visual areas and both hemispheres synchronize cells. Visual field feature produces coherent 40-Hz oscillations separated by as much as 7 mm in visual cortex [Eckhorn et al., 1988] [Eckhorn et al., 1993] [Engel et al., 1990] [Friedman-Hill et al., 2000] [Gray and Singer, 1989] [Kreiter and Singer, 1992] [Ritz and Sejnowski, 1997].
Somatosensory and motor cortex potentials synchronize while thinking but vanish during actual movement.
cause
40-Hz oscillations happen when cells in different cortex or thalamus parts respond to linked stimulus parts [Crick and Koch, 1990] [Engel and Singer, 2001] [Metzinger, 2000].
attention
Oscillations synchronize more during focused attention [Mountcastle et al., 1981] [Wurtz et al., 1982].
induced gamma wave
When people perceive object with coherent features, 30-Hz EEG wave starts in occipital cortex 200 ms after stimulus and dies out after perceptual processing.
People can measure magnetic fields caused by brain electric currents {magnetoencephalography} (MEG), using superconducting quantum interference devices (SQUID).
When people make or observe voluntary movement, EEG waves {mu wave} {µ wave} decrease. Mirror neuron activity blocks mu waves.
EEG waves {N400 wave} can be about semantic improbability, as opposed to semantic relatedness.
260 ms to 500 ms after rare stimuli, attention to object to recognize it or use it causes 40-Hz oscillations {P300 wave}, which correlate with event unexpectedness.
If people are conscious or dreaming, high-amplitude electrical waves {PGO wave} arise in pons, radiate to geniculate body, and then go to occipital cortex. Saccadic eye movements cause potential waves in cholinergic neurons in pons and go to lateral geniculate nucleus and occipital cortex. Signals from aminergic cells inhibit cholinergic neurons. PGO waves accompany desynchronization.
0.8 second earlier than planned voluntary movement, ipsilateral motor cortex EEG changes potential {readiness potential} to negative. Conscious willing feeling is later. 0.5 second earlier than unplanned voluntary movement, EEG changes potential to negative. Perhaps, consciousness can still stop or allow action before it has begins [Libet, 1993] [Libet et al., 1999]. Lateralized readiness potential is in contralateral cortex and happens after action selection.
For activation, awake stage and REM sleep has high-frequency low-amplitude EEG waves. NREM sleep has low-frequency high-amplitude EEG waves. Stage II NREM sleep has distinctive EEGs {sleep spindle} {K-complex wave}.
EEG waves {theta wave} in hippocampus can have frequency range 4 Hz to 8 Hz [Buzsáki, 2002] [Kahana et al., 1999] [Klimesch, 1999] [O'Keefe and Recce, 1993]. Theta-wave frequency increases until two to five years old. REM sleep has theta waves in hippocampus.
Treatments {Transcranial Magnetic Stimulation} (TMS) can excite or inhibit brain regions to treat depression, obsession, stress, and mania [Cowey and Walsh, 2001] [Kamitani and Shimojo, 1999].
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Date Modified: 2022.0225