Neuroscience Techniques January 22 2016 Lesion Studies The most famous lesion study was done by Paul Broca He examined a man named Tan who did not say anything other than tan Broca found a large lesion in a region of frontal cortex Broca s area that is responsible for language production Lesion Studies Carl Wernicke was a German neurologist who studied stroke victims He found that people who had a stroke that damaged part of temporal cortex could produce speech but not understand it Positron Emission Tomography PET Scan The most common form of a PET scan begins with an injection of a glucose based radiopharmaceutical FDG which travels through the body eventually collecting in the organs and tissues targeted for examination The patient lies flat on a bed table that moves incrementally through the PET scanner The scanner detects the gamma rays emitted from the patient to generate a picture of the areas of the brain that are most active This is a functional image of the brain Subtractive PET Scans of Brain Activation in Complex Language Tasks CAT Scan A computerized axial tomography scan or CAT scan is a procedure which uses a computer for combining many x ray images into crosssectional views of the internal organs of the body including the brain CAT scans are used to image both normal and abnormal structures in the body and can also be used to help guide the placement of instruments or treatments The CAT scanner is a large donutlike machine that takes x ray images at many different angles around the head in the case of brain imaging CAT Scan These images are processed by a computer and the resulting pictures look like slices tomo means slice taken through the head and brain Images of interest are first displayed on the computers screen but can later be transfered to film To imagine the slices through the brain visualize the head as a loaf of bread and you are looking at one end of the loaf i e at the top of some s head As you remove each slice of bread you can see the entire surface of that slice from the edge crust to the center A CAT scan produces a structural picture of the brain Magnet Resonance Imaging MRI When placed in a magnetic field the hydrogen atom has a strong tendency to line up with the direction of the magnetic field The MRI machine applies a radio frequency RF pulse that is specific only to hydrogen The system directs the pulse toward the area of the body to be examined The pulse causes the protons in that area to absorb the energy required to make them spin in a different direction This is the resonance part of MRI The RF pulse forces them only the one or two extra unmatched protons per million to spin at a particular frequency in a particular direction The specific frequency of resonance is calculated based on the particular tissue being imaged and the strength of the main magnetic field Magnet Resonance Imaging MRI When the RF pulse is turned off the hydrogen protons begin to slowly relatively speaking return to their natural alignment within the magnetic field and release their excess stored energy When they do this they give off a signal that the coil now picks up and sends to the computer system What the system receives is mathematical data that is converted into a picture That is the imaging part of MRI Magnet Resonance Imaging MRI When the RF pulse is turned off the hydrogen protons begin to slowly relatively speaking return to their natural alignment within the magnetic field and release their excess stored energy When they do this they give off a signal that the coil now picks up and sends to the computer system What the system receives is mathematical data that is converted into a picture That is the imaging part of MRI Functional MRI fMRI Functional Magnetic Resonance Imaging or fMRI is the use of MRI to learn which regions of the brain are active in a specific cognitive task as in speech or in the conjugation of a verb When the neurons in your brain are active they metabolize oxygen from the surrounding blood Approximately 6 seconds after a burst of neural activity a hemodynamic response occurs and that region of the brain is infused with oxygen rich blood Because oxygenated hemoglobin is diamagnetic while deoxygenated blood is paramagnetic MRI is able to detect a small difference a signal of the order of 3 between the two This is called a blood oxygen level dependent or BOLD signal The precise nature of the relationship between neural activity and the BOLD signal is a subject of current research Electrical Potentials of the Human Nervous System Event Related Potentials ERP