Recording of electrical activity / electrical stimulation of brain tissue Spike trains Spikes.
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Transcript of Recording of electrical activity / electrical stimulation of brain tissue Spike trains Spikes.
Recording of electrical activity / electrical stimulation of brain tissue
Spike trains
Spikes
Quiroga, Mukamel, Isham, Malach & Fried. PNAS 2008
Spiking activity in hippocampus and visual awareness
Positron emission tomography (PET) – Enables tracking metabolic processes in various brain
regionsInvolves injection of a radio-active tracerEnables scanning in multiple planes
1. Seeing words2. Listening to words3. Saying words4. Generating verbs
PET-Positron Emission tomography
1 2
3 4
Radioactive tracers – 2-deoxy-glucose (2DG) or Oxygen (in water)
Functional Magnetic Resonance Imaging
What does the fMRI signal measure?
• Hemoglobin has two states: Oxygenated (diamagnetic), andDe-Oxygenated (paramagnetic)
• The BOLD fMRI signal is sensitive to the ratio between Oxy and De-oxy hemoglobin in a manner that an increase in Oxygenated blood results in an increase in the fMRI signal.
Following neural activation:
Consumption of oxygen
Overcompensation with fresh oxygenated blood
Time
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fMRI signal
Time scale of fMRI signal (low temporal resolution)
fMRI allows detection of active regions during various functional tasks
VISUAL STIMULUS
1.5 T GE Scanner
Coil
Brain-Voyager Software
Epson LCDProjector
Experimental Setup
Generating a 3-D Model of the brain
Right eye Left eyePerception
Tong et al. 1998
Using fMRI to correlate brain responses and perception/behavior
Advantages of fMRI over PET
• Higher temporal resolution (seconds vs min)• No radioactive radiation• cheaper
Optical imaging
Intrinsic optical imaging: Oxy/deoxy hemoglobin have different properties regarding light absorbance
Voltage sensitive dyes
Temporal resolution: msSpatial resolution: ~50 µm
ElectroEncephaloGram (EEG)
Non invasiveUser friendlyHigh temporal resolutionLow spatial resolution
EEG - ElectroEncephaloGraphy
•Amplitude• Frequency
awake
time
volta
ge
Nir & Tononi 2010
• EEG global electrical activity– ERP: Event-Related Potentials:
W. W. Norton
High temporal resolution
Event-Related Potentials
Faces N170
W. W. Norton
EEG/ERP
• WHEN does the brain do it?– Temporal resolution: HIGH
• WHERE does the brain do it?– Spatial resolution: LOW
MEG
Temporal resolution: msSpatial resolution: few mm
Techniques & ResolutionsResolutions of functional techniques
Stimulation
1. Electrical
2. Chemical
3. Magnetic
4. Optical
Electrical stimulation (functional mapping)
Depth electrodes
Intracranial EEG (iEEG) Spikes
Electro-corticogram (ECoG)
Both electrode types can be used for either recording or stimulating
Chronic stimulation (Parkinson’s)
http://www.youtube.com/watch?v=FD8ckoy9NVU&feature=related
Mapping of speech area in a human patient
Chemical stimulation/blocking (kianic acid / muscimol)
Transcranial Magnetic Stimulation (TMS)
Single pulse – excitatory (MEP in motor cortex, Phosphenes in visual cortex)rTMS (repetitive TMS) – mostly inhibitory
Optogenetics
http://www.nature.com/nmeth/video/moy2010/index.html
1. Light sensitive channels (from algae or bacteria)
2. Introduce the engineered gene into a carrier virus
3. Inject the virus to the brain
4. Use light to switch the channels/cells on or off