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

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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

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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