Probing the Brain

Marr’s Three Level of Analysis

1. Computation(why/goal)

2. Algorithm (what/rules)

3. Implementation (how/physical)

Correlation vs Causation

Association or direct cause?

X-Ray Photography

• High-energy, short-wavelength lgight passes though sot tissue, absorbed by bone and dense structures

• Differential absorption creates contras

• Limitation: poor soft-tissue contrast for brain; ionizing radiation damages DNA

CAT(CT) Scan

• 3D x-ray images

• Non-inasive

• Very high exposure to radiation

MRI

Magnetic Resonance Imaging

EEG (Electro-encephalography)

Electrodes on the scalp meausre summed electrical fields from millions of neurons firing in coordination

• High temporal resolution; poor spatial resolution

ECoG (Electrocorticography

placed under the skull, directly on cortical surface

• research on language, memoyr and speech; pre-surgical epilepsy mapping

• Highly invasive, only performed on patients who require surger for clinical reasons

fMRI (function MRI)

Neural activity → metabolic demand → local increase in oxygenated blood → detectable change in MR signal

In-vivo Calcium Imaging

In-vivo fluroescent imaging of neural activity; uses an engineered molecule(GCaMP)

Transcranial Magnetic Stimulation (TMS)

rapidly changing magnetic field indusces an electrical current in the underlying cortex — briefly direxpts normal activity

• treatment-resistant OCD and smokingg ccesation, chronic pain, anxiety

• Limitation: surface cortext only; stimulatig a region also disrupts connections

Deep Brain Stimulation (DBS)

Surgically implanted electrodes deliver contrinuous electrical stimulation to deep brain structures (highly invasive)

• Limitation: stimulates all cells and fibers without much specificity

Optogenetics

technique that uses light tot control the activity of genetically defined neurons (genetics + optics + neuroscience)

• Can control neural activity with teh switch of a light