PSYCH 454 Lecture Notes - Lecture 22: Sensory Cortex, Visual Cortex, Low Frequency
24 May 2018
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Lect 22: Consciousness part 3
Rhythms and Frequency
●Frequency: also called “waves’ or oscillations
○Can measure by amplitude (how tall/large fluctuations) or by phase (what stage
that wave is across cycle, up or down)
○1 cycle = 1 up and down
●1 cycle/second= 1 Hz
○1 or 3 cycles/second = delta (1-4 Hz)
○6 cycles/second= theta (4-8 Hz)
Waves/oscillations and Frequency
●12 cycle /sec = 24Hz → alpha (8-13Hz)
●24 Hz→ Beta (13-30Hz)
●48 Hz → Gamma (30-70 Hz)
●Be aware that there are different frequency ranges according to cycles/sec
Frequencies commonly associated with specific cognitive functions
●Delta (1-4 Hz): low vigilance states: sleep, anesthesia
○Role in cognition?
●Theta (4-8 Hz): memory processing
○Prominent theta oscillations in, but not only, hippocampus
●Alpha (8-13 Hz): visual attention; even if eyes are closed
○Prominent in visual cortex
, as well as fronto-parietal cortex
●Beta (13-30 Hz): motor processing
○Prominent in motor cortex (and feedback paths?) → info from higher order
areas (cortex) back to sensory areas (alpha and beta)
○Deep layers of cortex (layer 5 and 6)
●Gamma (30-70 Hz): sensory evoked processing, correlate of conscious awareness
and
more
○Commonly seen in many brain areas (+ feedforward paths)
○Especially in superficial layers (layers 1-3) → info from lower order areas to
higher order areas
EEG Rhythms during Sleep ** WILL BE ON EXAM **
●EEG frequency decreases
as anesthesia deepens
○Awake state: alpha and beta rhythms→ low amplitude, high frequency
○NON REM:
■Stage 1: theta (4-8 Hz)
Document Summary
Can measure by amplitude (how tall/large fluctuations) or by phase (what stage. 1 cycle = 1 up and down that wave is across cycle, up or down) 1 or 3 cycles/second = delta (1-4 hz) 12 cycle /sec = 24hz alpha (8-13hz) Be aware that there are different frequency ranges according to cycles/sec. Delta (1-4 hz): low vigilance states: sleep, anesthesia. Alpha (8-13 hz): visual attention; even if eyes are closed. Prominent theta oscillations in, but not only, hippocampus. Prominent in visual cortex , as well as fronto-parietal cortex. Prominent in motor cortex (and feedback paths?) Info from higher order areas (cortex) back to sensory areas (alpha and beta) Deep layers of cortex (layer 5 and 6) Gamma (30-70 hz): sensory evoked processing, correlate of conscious awareness and more. Commonly seen in many brain areas (+ feedforward paths) Especially in superficial layers (layers 1-3) info from lower order areas to higher order areas.
