EEG, Event-related potential (ERP), Magnetoencephalography (MEG) Exam q: which setup will you use to measure activity in the occipital cortex in a blind patient?

Brain Imaging Techniques fMRI or functional magnetic resonance imaging Measures brain activation by detecting the increase in oxygen levels in active structures. Advantages: activity measurement, good spatial resolution and speed, no radioactive substances Disadvantage: unable to resolve details at the all-important circuit level. Brain imaging tracks the power consumption of a million neurons, irrespective of whether they are excitatory or inhibitory, project locally or globally, and so on. SOURCE: Reprinted with permission from “Building Memories: Remembering and Forgetting of Verbal Experiences as Predicted by Brain Activity” by A.D. Wagner et al., Science, 281, p. 1188-1191. © 1998 AAAS

CT or computed tomography: A dye is injected into the blood. A series of X-rays is made from different angles; the images reflect the density of blood vessels in each area. A computer combines the X-rays into a series of horizontal sections of the brain.

PET or positron emission tomography Injecting radioactive substance into the bloodstream, which is taken up by active parts of the brain. Advantages: ability to track changing activity in the brain, fast Disadvantages: expensive, requires sophisticated staff, must be near a cyclotron, relatively slow

Research Techniques: Autoradiography reveals which neurons are active Adapted from Tootell, 1982 Macaque monkeys were trained to stare at a pattern (left panel) while injected with radioactive glucose (14Clabeled 2-deoxy-D-glucose). The radioactive glucose was absorbed and metabolized by active neurons to a much greater extent than by other neurons. After the experiment, the animals were sacrificed and the cortical radioactivity pattern was analyzed. This method provides high resolution radioactive labeling of active neurons. The physical pattern of active neurons (right panel, darker pixels correspond to greater neuronal activity) is clearly a geometrical representation of the pattern physically laid-out on the cortex. This experiment clearly demonstrates that the visual cortex relies on topographical representation of spatial information Macaque monkeys were trained to stare at a pattern (left panel) while injected with radioactive glucose. The radioactive glucose was absorbed and metabolized by active neurons to a much greater extent than by other neurons. After the experiment, the animals were sacrificed and the cortical radioactivity pattern was analyzed. This method provides high resolution radioactive labeling of active neurons. The physical pattern of active neurons (right panel, darker pixels correspond to greater neuronal activity) is clearly a geometrical representation of the pattern physically laid-out on the cortex. This experiment clearly demonstrates that the visual cortex relies on topographical representation of spatial information.

EEG, Event-related potential (ERP), Magnetoencephalography (MEG) Exam q: which setup will you use to measure activity in the occipital cortex in a blind patient?

An Electroencephalograph EEG / electroencephalogram records the combined activity from many neurons (irrespective of whether they are excitatory or inhibitory, project locally or globally, and so on) by using multiple electrodes; has excellent temporal resolution but poor spatial resolution; is best used to detect changes in arousal. Garrett: Brain & Behavior 4e

EEG: Epilepsy Epilepsy (from the Ancient Greek meaning "to seize") is a group of neurological disorders characterized by epileptic seizures. Prevalence: 1 in 100 Epileptic seizures are episodes that can vary from brief and nearly undetectable to long periods of vigorous shaking. Often brought on by factors such as lack of sleep, stress or flickering light among others. In epileptic seizures a group of neurons begin firing in an abnormal, excessive, and synchronized manner. Patient HM. The Brain: Teaching Modules. (1997). http://www.learner.org/resources/series142.html : 30. Understanding the Brain Through Epilepsy

Garrett: Brain & Behavior 4e EEG and Evoked Potentials Figure 4.9: Evoked Potential Produced by a Novel Tone Evoked potential measurement: uses a computer to average the EEG over several stimulus presentations; cancels out the “noise” of the brain’s other activity, leaving only the unique response to the stimulus. Garrett: Brain & Behavior 4e

Magnetoencephalography Origin of the brain's magnetic field.

Permits excitation or inhibition. Transcranial magnetic stimulation is used to induce a transient interruption of normal activity in a relatively restricted area of the brain. It is based on the generation of a strong magnetic field near the area of interest, which, if changed rapidly enough, will induce an electric field sufficient to stimulate neurons. Permits excitation or inhibition. It is showing promise as a therapeutic tool as well as in research

Exam q: which setup will you use to measure activity in the occipital cortex in a blind patient?

Research Techniques Figure 4.7: Scanning Electron Microscope Light microscopes: Cell bodies, dendrites, axons, and large organelles in neurons; Limited capability due to the nature of light. Electron microscopes: Pass beams of electrons through a thin slice of tissue onto detector; High resolution, magnifying objects up to 250,000 times; can reveal objects in 3-D (scanning electron microscope). Garrett: Brain & Behavior 4e

Single unit recording

Whole-cell patch-clamp

Intracellular electrodes