- Normal Awake
- Normal Drowsiness, Sleep, Arousal: Adults
Normal Awake:Adults
Alpha Rhythm (Figs. 52 to 60, 63, 64, 66 to 71)
- 9 to 13 Hz; slows to 7 to 8 Hz in drowsiness.
- Sinusoidal or sharply contoured if beta present.
- Waxing and waning–that is, “beating”–if composed of two close frequencies, such as 9 and 10 Hz.
- Same dominant frequency in each hemisphere.
- Highest amplitude O1,2; P3,4; T5,6.
- Commonly extends to C3,4; A1,2; T3,4.
- Bilaterally symmetrical or higher right most common. Higher left also normal.
- Persistent symmetry >50% produced by artifact or abnormality.
- Symmetry is variable within recording.
- Ear referential recording is the best measure of symmetry.
- Partial or complete “blocking” by eye opening or alerting; attenuation normally symmetrical.
- Low voltage ( (
 Fig 52 |  Fig 53 |  Fig 54 |  Fig 55 |
 Fig 56 |  Fig 57 |  Fig 58 |  Fig 59 |
 Fig 60 |  Fig 63 |  Fig 64 |  Fig 66 |
 Fig 67 |  Fig 68 |  Fig 69 |  Fig 70 |
 Fig 71 |  Fig 77 |
Posterior Slow Waves of Youth (Figs. 61 and 62)
250- to 400-ms monophasic waves. Principally O1, O2. Interrupts alpha activity, creating sharply contoured waves. Adolescents, children, young adults
 Fig 61 |  Fig 62 |
Slow Alpha Variant
Saw-toothed waveforms at about one-half alpha frequency from partial fusion of two alpha waves. Same location and reactivity as alpha.
Mu Rhythm (Figs. 58 and 65)
Arciform–apiculate negative and rounded positive phases. 10 (9 to 11) Hz. Intermingled with 20-Hz beta. C3,4 and Cz location; occasionally involves P3,4. Long epochs of unilateral expression common.
Normal if other central rhythms symmetrical. Side-to-side shifts in maximal amplitude occur. Movement of contralateral or ipsilateral extremities (or its contemplation) blocks rhythm. Eye opening has no effect. High voltage over skull defect–breach rhythm. Apiculate phase may resemble spikes.
| Fig 58 |  Fig 65 |
Beta (Figs. 68, 72 to 76)
Any rhythmic activity >13 Hz.
Some beta in all normals; amount varies. 14 to 40 Hz, 15 to 25 Hz most common. Usually sinusoidal; apiculate or arciform if competing frequencies; “beating” if close frequencies. May occur in bursts. Locations Frontal: common. Central: common, mixed with mu. Posterior: fast alpha variant. Diffuse: when abundant medication effect. Usually Amplitude and distribution increased by: Drowsiness, light sleep, rapid eye movement (REM) sleep. Skull defect. Medication; especially benzodiazepines, barbiturates. Diffuse theta may accompany medication-induced excess beta.
Theta Low-voltage
( It is more common in children and young adults than in older adults. Temporal theta. ≤10% of awake records in normal subjects over 60 years. Equal distribution bilaterally or twice as abundant on left. Single wave or brief bursts separated by normal background.
| Fig 68 |  Fig 72 |  Fig 73 |
 Fig 74 |  Fig 75 |  Fig 76 |
Hyperventilation (Figs. 78 to 80)
Sequence: Increase in diffuse theta.
Rhythmic delta in bursts. Continuous rhythmic delta. Effect maximal anteriorly in most adolescents and adults. Maximal amplitude of delta bursts may shift from side to side. Multiple frequencies may create apiculate waveforms. Effect greatest in youth, with maximal effort and low serum glucose. Effect subsides in 60 to 90 s after hyperventilation (HV). May abnormally elicit focal spikes, generalized spike–waves, and focal delta or theta. Post-HV period may contain newly appearing focal delta or theta as abnormalities.
 Fig 78 |  Fig 79 |  Fig 80 |
Lambda Waves (Fig. 81)
O1,2 principally; involve P3,4 and T5,6. Bilaterally synchronous. Diphasic or triphasic. Largest wave electropositive, lasting 100 to 200 ms. Usually50 µV. Evoked by scanning well-illuminated, patterned visual field. Present in 50% of normal EEGs.
Fig 81
Photic Stimulation (Figs. 82 to 84)
≤3 flashes per second. Electropositive evoked response. 100-ms delay. Maximum O1,2 and T5,6. Variable anterior extension. Resembles lambda. ≥6 flashes per second. More rhythmic response. Time-locked to flash with harmonic or subharmonic frequencies. Initial response may resemble (a) response of ≤3 flashes per second, (b) lambda, or (c) V-wave. Responses larger in children and the elderly. Responses symmetrical or asymmetrical, usually higher right. Responses not visible in many normal subjects.
 Fig 82 |  Fig 83 |  Fig 84 |
Wicket Spikes
Arciform waves. Negative phase apiculate. Positive phase rounded. Single or clusters. T3,4, or T3,4 to F7 or F8. Unilateral or independent bilateral. No distortion of background rhythms.
Psychomotor Variant–Rhythmic Temporal Waves
5 to 7 Hz. Sharply contoured, often notched. Mid-anterior temporal regions. Parasagittal spread. Bursts or runs. Gradual onset and offset. Monomorphic; that is, without evolution.
Subclinical Rhythmic EEG Discharge of Adults (SREDA)
Sequential monophasic or biphasic apiculate waves mixed with rhythmic theta or delta. No morphological evolution. Abrupt onset; abrupt or gradual offset. Usually in wakefulness, occasionally in sleep. May occur after HV. Principally parietal, posterior temporal. Bisynchronous or unilateral. Occurs principally in elderly or middle age.
Normal Drowsiness, Sleep, Arousal:Adults Drowsiness (Figs. 125 to 130)
Theta augments in amplitude and distribution and is rhythmic. Alpha augments in amplitude and distribution, then disappears. Beta increases, occasionally in bursts, then may decrease. Slow lateral eye movements. Occasional 2 to 4 Hz waves, in bursts, in the elderly. Brief epochs of drowsiness common in senility.
 Fig 125 |  Fig 126 |  Fig 127 |  Fig 128 |
 Fig 129 |  Fig 130 |
Vertex (V) Waves (Figs. 131 to 133, 135 to 140)
Bilaterally synchronous.
Maximal amplitude at vertex (Cz). Extend to Fz, Pz; F3,4; C3,4; P3,4. May appear in sequences. Shifting asymmetries occur. Principal component is usually a sharply contoured electronegative wave. Principal component may be positive. May be preceded and/or followed by smaller waves of opposite polarity. Highest amplitude and sharpest in youth; become more blunt with age. Appear principally in light sleep but also in wakefulness, drowsiness, and at onset of high-frequency flash stimuli. Rarely suppressed by focal pathology.
 Fig 131 |  Fig 132 |  Fig 133 |  Fig 135 |
 Fig 136 |  Fig 137 |  Fig 138 |  Fig 139 |
 Fig 140 |
Spindles (Figs. 136, 137, 139 to 141)
Rhythmic or arciform waves. In 2 to 3 s bursts, waxing and waning, giving spindle shape. Bilaterally synchronous and symmetrical or asynchronous with symmetry of total spindle quantity. 13 to 14 Hz, Cz,3,4 with frontal spread in light stage 2 sleep. 10 to 12 Hz, Fz,3,4 in deeper stage 2 and stage 3 sleep.
| Fig 136 | Fig 137 | Fig 139 |
| Fig 140 |  Fig 141 |
Mitten Pattern (Figs. 138 and 139)
High-voltage 400 to 500 ms waves at Fz-Cz with parasagittal spread. Notched in ascending phase by 100 to 125 ms wave.
| Fig 138 | Fig 139 |
K Complexes
Diphasic wave. Initial brief wave. Subsequent slower wave. Spindles superimposed on slower wave.Stage 2 sleep.
Rapid Eye Movement (REM) Sleep (Figs. 144 to 146)
Low voltage. Mixed frequencies: theta, beta, delta. Clusters of rapid conjugate vertical and/or horizontal eye movements.
 Fig 144 |  Fig 145 |  Fig 146 |
Deep Sleep (Figs. 142 and 143)
Diffuse delta. Minimal spindles, no V waves.
 Fig 142 |  Fig 143 |
Arousal (Figs. 155 and 156)
Number, complexity, and duration of phenomena vary directly with depth of sleep. From drowsiness: abrupt with minimal or no intermediate theta/delta waves or frontocentral beta. From light sleep: V waves. Frontocentral alpha–theta. From deep sleep: High-voltage delta. Frontocentral alpha–theta. Duration: 1–2 s from light sleep; 3–5 s in deep sleep.
 Fig 155 |  Fig 156 |
Small Sharp Spikes (Figs. 149 to 152)
Abrupt ascending slope. Steeper descending slope. Followed by low-amplitude slow wave, same polarity as spike; or low-amplitude potential as “dip” in background, polarity opposite to spike. Brief: No disruption of background activity. Widespread field; dipole between hemispheres or within hemisphere. Cancellation between ear (Al,2) and posterior temporal lead (T5,6) common.
Often appear bilaterally with maximal amplitude in one hemisphere. Single events; rarely as doublets. Appears in adults and adolescents. Light, non-REM sleep. Appears in multiple channels on common average reference montage (CAR).
 Fig 149 |  Fig 150 |  Fig 151 |  Fig 152 |
6-per-Second Spike Waves (Figs. 153 and 154)
5 to 7 Hz. Brief, low-amplitude spike. Awake or drowsy; not sleep. Waves are bisynchronous. Two forms: Low-amplitude, posterior. High-amplitude, anterior.
 Fig 153 |  Fig 154 |
Fig 134
Normal Drowsiness, Sleep, Arousal:Adults Drowsiness (Figs. 125 to 130)
Theta augments in amplitude and distribution and is rhythmic. Alpha augments in amplitude and distribution, then disappears. Beta increases, occasionally in bursts, then may decrease. Slow lateral eye movements. Occasional 2 to 4 Hz waves, in bursts, in the elderly. Brief epochs of drowsiness common in senility.
| Fig 125 | Fig 126 | Fig 127 | Fig 128 |
| Fig 129 | Fig 130 |
Vertex (V) Waves (Figs. 131 to 133, 135 to 140)
Bilaterally synchronous.
Maximal amplitude at vertex (Cz). Extend to Fz, Pz; F3,4; C3,4; P3,4. May appear in sequences. Shifting asymmetries occur. Principal component is usually a sharply contoured electronegative wave. Principal component may be positive. May be preceded and/or followed by smaller waves of opposite polarity. Highest amplitude and sharpest in youth; become more blunt with age. Appear principally in light sleep but also in wakefulness, drowsiness, and at onset of high-frequency flash stimuli. Rarely suppressed by focal pathology.
| Fig 131 | Fig 132 | Fig 133 | Fig 135 |
| Fig 136 | Fig 137 | Fig 138 | Fig 139 |
| Fig 140 |
Spindles (Figs. 136, 137, 139 to 141)
Rhythmic or arciform waves. In 2 to 3 s bursts, waxing and waning, giving spindle shape. Bilaterally synchronous and symmetrical or asynchronous with symmetry of total spindle quantity. 13 to 14 Hz, Cz,3,4 with frontal spread in light stage 2 sleep. 10 to 12 Hz, Fz,3,4 in deeper stage 2 and stage 3 sleep.
| Fig 136 | Fig 137 | Fig 139 |
| Fig 140 | Fig 141 |
Mitten Pattern (Figs. 138 and 139)
High-voltage 400 to 500 ms waves at Fz-Cz with parasagittal spread. Notched in ascending phase by 100 to 125 ms wave.
| Fig 138 | Fig 139 |
K Complexes
Diphasic wave. Initial brief wave. Subsequent slower wave. Spindles superimposed on slower wave.Stage 2 sleep.
Rapid Eye Movement (REM) Sleep (Figs. 144 to 146)
Low voltage. Mixed frequencies: theta, beta, delta. Clusters of rapid conjugate vertical and/or horizontal eye movements.
| Fig 144 | Fig 145 | Fig 146 |
Deep Sleep (Figs. 142 and 143)
Diffuse delta. Minimal spindles, no V waves.
| Fig 142 | Fig 143 |
Arousal (Figs. 155 and 156)
Number, complexity, and duration of phenomena vary directly with depth of sleep. From drowsiness: abrupt with minimal or no intermediate theta/delta waves or frontocentral beta. From light sleep: V waves. Frontocentral alpha–theta. From deep sleep: High-voltage delta. Frontocentral alpha–theta. Duration: 1–2 s from light sleep; 3–5 s in deep sleep.
| Fig 155 | Fig 156 |
Small Sharp Spikes (Figs. 149 to 152)
Abrupt ascending slope. Steeper descending slope. Followed by low-amplitude slow wave, same polarity as spike; or low-amplitude potential as “dip” in background, polarity opposite to spike. Brief: No disruption of background activity. Widespread field; dipole between hemispheres or within hemisphere. Cancellation between ear (Al,2) and posterior temporal lead (T5,6) common.
Often appear bilaterally with maximal amplitude in one hemisphere. Single events; rarely as doublets. Appears in adults and adolescents. Light, non-REM sleep. Appears in multiple channels on common average reference montage (CAR).
| Fig 149 | Fig 150 | Fig 151 | Fig 152 |
6-per-Second Spike Waves (Figs. 153 and 154)
5 to 7 Hz. Brief, low-amplitude spike. Awake or drowsy; not sleep. Waves are bisynchronous. Two forms: Low-amplitude, posterior. High-amplitude, anterior.
| Fig 153 | Fig 154 |
Fig 134
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