Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
Brain Waves
Glenn Blanche/e
CNS Oscilla4on Frequencies
Theta 4-‐8Hz prefrontal cortex & hippocampus, memory & awareness
Alpha 8-‐12Hz sensory cortex & thalamus, percep4on & a/en4on
Beta 12-‐30Hz subthalamic n., basal ganglia & motor cortex, motor control
Gamma 30 -‐ Hz all structures, synchronisa4on & co-‐ordina4on
Spiking Neuron Model
• Why should phase have any influence on ERP?
• ui(t) = ΣjΣf Jijeij (t – tj – Δij) + urest
Measuring Phase Rela4onships
• How to determine phase in an EEG?
• How to quan4fy the rela4onship with ERP? PLV = 1/n Σ e2πiφ
The phase of ongoing EGG oscilla4ons predicts visual percep4on. Busch NA 2009 J Neuroscience 29: 7869 -‐ 76
• First paper looking at wave phase preceding event
• Method – 12 subjects – Luminescence calibrated threshold s4mulus – Scalp EEG 32 track -‐ whole spectrum 4 – 200 Hz
– Repor4ng • PLVs • Bifurca4on index
• Results – ERPs strongly correlate with percep4on (p < 0.001) – Confirms other work: power associated with 12% diff
– Main result: phase associated with 16% of difference.
• Cri4que – Method too simple – guessed events
– Difficulty with measuring phase & PLV – Difficult to read, complicated discussion of measurement
– Poor result
Synchroniza4on of neural ac4vity across cor4cal areas correlates with conscious percep4on. Melloni L 2007 J Neuroscience 27: 2858 -‐ 65
• First paper suppor4ng global synchronisa4on as a basis for conscious percep4on
• Method – 20 subjects – Masked second word, 4me threshold
– Two language based tasks: word & congruence matching
– Scalp EEG 64 track – gamma band – Reports phase synchron. between paired electrodes – See topographical maps
• Results – Confirms Busch: higher ERP related to gamma phase – Objec4ve processing of visible & ‘invisible’ words – Global processing – synchronised gamma phase (p < 0.04) – Short dura4on 100ms
• Cri4que – Very clever method – Interes4ng discussion of cause or effect – Significance of main result?
Driving fast-‐spiking cells induces gamma rhythm and controls sensory responses. Deisseroth K 2009 Nature 459: 663 -‐ 67
• Ground breaking experimental model – Gene4cally engineered mice
– Light sensi4ve bacteriorhodopsin gene (ChR2) – Introduced by viral vector into PV interneurons in barrel cortex – Labelled with fluorescent an4body – Direct driving of inhibitory GABA interneurons by blue/yellow light
• Method – 5 mice, implanted CNS electrodes, direct applica4on light sorce
– Descrip4ve study (sample phases)
• Results – Showed inhibitory driving produced gamma oscilla4on
– Ga4ng, refractory period – Confirmed sensory awareness
related to gamma phase
• Cri4que – Very interes4ng paper, founda4on for future inves4ga4ons – Invasive procedure – Descrip4ve vs hypothesis tes4ng
Frequency of gamma oscilla4ons routes flow of informa4on in the hippocampus. Colgin LL 2009 Nature 462: 353 -‐ 57
• Inves4gates co-‐ordina4on between mul4ple regions via different frequencies
• Method – 16 LE rats, implanted CNS electrodes – Sampled EEG in three regions: MEC, CA3, CA1
– Measured synchronisa4on of frequency oscilla4on between regions.
• Results – MEC – CA1 PLV associa4on 40% fast gamma (0% slow) transfer of current posi4onal informa4on
– CA3 – CA1 associa4on 53% slow gamma (32% fast) fast gamma – storage, slow gamma retrieval
• Cri4que – Associa4on doesn’t prove conjecture – Difficult to read
Clinical Correla4on
• Schizophrenia – Impairment in cogni4ve func4on & working memory – Reduced GABA synthesis in PV inhibitory interneurons in pre-‐frontal cortex – Reduced gamma frequency synchronisa4on
– Inherited condi4on in up to 60% – Pharmacological treatment using selec4ve GABA agonists
• Review: Cor4cal Inhibitory Neurons and Schizophrenia Lewis DA 2005 Nature Reviews Neuroscience 6:312 -‐ 324