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Dominant (“alpha”) rhythm
• Normal EEG pre-school to Adolescence Occipital rhythm
• 3-4 Hz activity at 3-4 months of age– responds to stimulation at 5-6 mo.
• At 6 mo, typically 5-6 Hz• At 1 year, 6-7 Hz.
• Frequency range increases as child ages. • Typical 10y old averages about 10 Hz.
Neurometic Analysis(Comparing someone to a QEEG Database to identify statistical
abnormality, commonly > 2 Std deviations, plus or minus)
• Baseline conditions– Eyes closed– Eyes open– Motor control– Stimulus control
• Task conditions or challenge conditions– Problem solving– Performance
Correct for state transitions
Stabilize state before recording, and include stabilization in database!
Look at the data
More is better
(Some db use 30 s only)
Criticisms of Neurometrics
• Color maps are deceptive1
• Too many statistical tests (inflating Type I errors)
• Some normals appear abnormal to controls
• Overly sensitive to artifact• More removed from the data,
the more errors that can creep in– E.g., unreliable discriminant
functions
• Methodology differences between client and database recordings
• Artifact management differences
• Normative database not representative2
• Differences in basic parameters (power/magn), coherence calculation
Not ready for prime time …if misused!
Brain maps can be deceptive …..
Some activation needed at left medial temporal site or right occipitoparietal juncture?
Deciphering Neural codingWe transform from time to frequency because we believe
mental or psychophysiological phenomena are best captured by latter domain
Brainwave frequencies and tentative mental correspondences
1
0.5 – 4 Hz DELTA Sleep
4-7 Hz THETA Inward focus, distracted, daydream
8-12 Hz ALPHA Relaxed, not actively processing
12-15 Hz SMR Relaxed, external attention (low beta)
15-18 Hz BETA Active external attention
19-35 Hz HIGH High correlation with anxiety, BETA intensity, or lots of muscle tension.
Activation is inversely proportional to alpha activity incidence
• To some extent, regardless of topography
Cerebral Organization Variation (and obstacles to neurometric assessment)
Trait and State variables
– TRAIT• Gender• Handedness• Age• Education• Experience• Neurological
present/history• Bilingual• Diagnosis!
– STATE• Task competence
– practice
• Task strategies• Time of Day• Drugs• Sleep debt
Measurement parameters
• Relative vs Absolute – Power/magnitude
• Connectivity or linear dependency – Asymmetry– Coherence, comodulation
Current EEG Applications
• CLINICAL• Epilepsy (1930s)• Sleep (1940s)• Patient monitoring, anaesthesia• Head injury assessment• Neurological assessment (AEP, ERP)• Neurotherapy• Psychiatric assessment
Current EEG Applications
• SCIENTIFIC
• Attention
• Workload
• Circadian rhythms
• Cognition
• Learning & Memory
• Neuroimaging co-registration