L16 Investigating the brain

• What is computerised tomography?

  1. A contrast dye is injected into the blood
  2. A series of x rays are sent out from different angles
  3. The scanner rotates slowly to take a measurement at each angle
  4. Radiation absorption varies with the tissue density
  5. From the measurements, a computer constructs images of the brain
• How does an MRI work?

  1. a powerful magnetic field is applied for a split second
  2. All atoms in the brain align to the magnetic field, then relax once it turns off realising electro-magnetic energy
  3. by measuring that energy, the 3D image of the brain is created
• What is an EEG?

  • Electrical brain activity is measured on the scalp in living people.
  • It is sensitive to postsynaptic dendritic currents generated by a population of neurons that are active in synchrony.
  • Excellent temporal resolution
  • Poor spatial resolution
• Mapping brain function: electrical brain stimulation

  • The brain is cut open with the patient under anaesthesia, then they are woken up and different parts of the brain are stimulated to see what is produced.

  
• Single cell recordings:

  • A tiny electrode is implanted in the brain and information is sent from this.
  • The electrode records activity of a single neuron
  • In cats, they found the part of the brain related to anger/ fear and when an electrical impulse was passed through it the cat showed anger/ fear, but when it stopped they were calm.
• Modern brain stimulation:

  • examines the effects of stimulating some brain areas\
  • TMS: neurons are excited/ inhibited by externally applying time-varying electromagnetic fields generated by a coil located above the head e.g. if auditory cortex is stimulated they could hear things.
• What are Event-related-potentials (ERPs)?

  EEG activity time-locked to an external event, averaged across multiple occurrences of the same event to reduce noise.

  ERp peak direction, amplitude and timing are used to investigate brain processes used in different cognitive domains.
• What is Magnetoencephalography (MEG)?

  A recording of magnetic fields produced by electrical currents in the brain using arrays of SQUIDs.
• How do fMRIs work?

  Measures activation by detecting the increase in oxygen levels:

  • active neurons consume oxygen and convert oxyhemoglobin into deoxyhemoglobin
  • measures the concentration of oxyhemoglobi in the blood.
  • The change in Blood oxygen level dependent contrast (BOLD) is known as the hemodynamic response function
• How do PET scans work?

  • measures local blood flow into a brain region
  • radioactive tracer injected into the blood stream
  • tracer takes up to 30 seconds to peak
  • based on blood volume