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March 9, 2021

[Brain Image]    

PSY 340 Brain and Behavior

Class 13: Research Methods in Neuropsychology

   


How do we learn about how the brain works?

In one of my classes a while ago, a student asked, "So, how do we know these things about the brain?" Indeed, how do we know that the occipital lobe deals with vision and the frontal lobe with working memory? Why can we say that the hippocampus is responsible for any new declarative memories, but NOT for procedural memories or learning like how to ride a bike?

Brain vs. Behaviors

1. Look at the Effects of Brain Damage

2. Stimulate Some Brain Area and Analyze the Resulting Behavioral Change

3. Record Brain Activity during Behavior

4. Correlate Brain Anatomy with Behavior




1. Look at the Effects of Brain Damage

   

broca_tanPaul Pierre Broca (1824-1880) 
  • Patient could only say, "tan, tan" after stroke. 
  • Autopsy of brain (see left) found damage to lateral posterior (side, rear area) of frontal lobe.
  • Broca's or expressive aphasia: inability or difficulty speaking clear language.

Stereotaxic Instrument

Animal Brain Research


Transcranial Magnetic Stimulation
Transcranial Magnetic Stimulation (TMS)

BBC The Brain: A Secret History

Michael Mosley has areas of his brain turned off by TMS (YouTube)





2. Stimulate Some Brain Area and Analyze the Resulting Behavioral Change

In the 19th & early 20th centuries, physiologists began to stimulate the brains of experimental animals (dogs in particular) by using an electrical stimulus. This research established that some important areas of the brain were responsible for certain sensory experiences and motor skills.

Rat (Optogenetics)Optogenetics = Using light to control a limited group of neurons




3. Recording Brain Activity during Behavior


[EEG of Child with Petit Mal Epilepsy]EEG (Electroencephalograph)


[EEG 1929]



PET Scan (Positron Emission Tomography)

PET ScanPET Temporal Lobe Hypoactivity
Subject is injected with slightly radioactive glucose (sugar). Brain tissue that is most active will use the glucose. A by-product of radioactive decay are two positrons which move in a straight line in opposite directions. Radiation detectors receiving the positron particles can help determine where in the brain the glucose was being used most heavily.



Functional Magnetic Resonance Imaging (fMRI)

fMRI of
            occipital lobeRegular MRIs (see below) tell us about the structure of the brain. In the last decade, though, functional MRI (fMRI) scanners can tell us about the functioning or activity of the brain. The scanners detect where blood is being used by focusing upon the hemoglobin molecule which gives up oxygen. This is called looking for the BOLD (= Blood Oxygen Level Dependent) signal.

In an fMRI scan, a baseline structural image (MRI) of the brain is taken. Then, the brain is scanned (1) when it is not doing any task (Scan 1) and then (2) when it IS doing a specific task or activity (Scan 2). Scan 1 is subtracted from Scan 2 in order to identify those areas which are particularly active during the task.

The image to the left shows the brain as an individual is focusing upon a complex moving visual image. The areas highlighted in yellow and orange represent greater levels of activity compared to when the individual is focused upon a blank screen.

Taken from http://en.wikipedia.org/wiki/Image:FMRI.jpg

Default Mode NetworkExamples of psychological findings from fMRI

A major difficulty with fMRI imaging is the problem of head movement. Even very small motions can cause the wrong areas of the brain to display when someone is doing a task.





4. Correlate Brain Anatomy with Behavior

Computerized Axial Tomography (CAT): Brief x-rays from 180 degrees around head
CAT ScanCAT Scan - hemorrhage

Images will show areas of damage. For example, in the CAT scan image on the right, the individual has experienced a cerebral hemorrhage (a type of stroke).

Magnetic Resonance Imaging (MRI): Body tissue is subjected to a strong magnetic field which is turned on and off rapidly in the presence of a radio wave. The atoms of the brain change their alignment (spin) because of the magnetic field when it is on and give off characteristic radio signal when it is turned off. A detector reads those signals and, using a computer, can map the structure of the tissue. There is NO radioactive materials used in an MRI.

MRIMRI (1319-25)

In the MRI image on the right, the patient appears to have a large tumor growing in the mid-portion of the brain. This has compressed the cingulate cortex and is pressing down on the corpus callosum.




Brain vs.
              Body MassBrain Size and Intelligence

1. Humans do not have the largest brains across animal species. We do not even have the largest ratio between brain size & body size.

2. Animals with larger brains often have larger neurons so that comparing the volume of animal with human brains is not equivalent.

3. Humans: Brains vs. IQ (Intelligence)
  • There is a moderate correlation between brain size and IQ tests (r = ~.30-40, which equals explaining about 9% to 16% of IQ differences due to size).
  • CAUTION: IQ test scores may not be adequate to evaluate "intelligence" which is a notoriously difficult concept to quantify.
    • Hevern: Intelligence involves those abilities to cope successfully with whatever environments (physical, interpersonal, or cultural) individuals find themselves in.
    • Because IQ tests only measure a range of cognitive functions appropriate for life in an industrialized or economically-developed world, they are not necessarily measures of the full range of coping abilities (=intelligence) that are associated with differing environments.
  • Males generally do have larger brains than females (roughly 8-10%). However, there are no overall IQ differences between men and women.
  • Males vs. Females
    • Differences of specific skills or ability levels between men and women are sometimes found. However, within the context of differing developmental pathways (boys and girls often experience growing up with different opportunities and emphases), many such differences are not biological, but actually cultural, e.g., the superiority of boys in math may reflect the opportunities boys take to take part in activities involving numbers or geometric shapes.
    • There are differences in the amount of gray vs. white matter across the sexes. Women have deeper & more sulci than men and, despite females brains being roughly 8-10% smaller in volume, there is equal cortical surface for men and women.
    • Some structural differences have been found in the wiring between female and male brains. The significance of these findings is not yet clear.
    • And, when such structural differences are found, it is not immediately clear that there is any relationship between such structural differences and actual behavioral outcome. For example, Liu et al. (2020) reported that males have a larger face processing cortical area than females; yet, studies such as Rennels & Cummings (2013) affirm that women do better than men in actual face processing tasks.


RESOURCES

Blow, N. (2009, April 16). Functional neuroscience: How to get ahead in imaging. Nature, 458, 925-928. doi: 10.1038/458925a; Available online at http://www.nature.com/nature/journal/v458/n7240/full/458925a.html

"Advances in magnetic resonance imaging are helping sciences learn more about the structure and function of the brain. Nathan Blow looks at how far the technology has developed and where it could go." (site blurb)

Deisseroth, K. (2015). Optogenetics: 10 years of microbial opsins in neuroscience. Nature Neuroscience, 18,(9), 1213-1225.

DeWitt, I., & Rauschecker, J. P. (2012). Phoneme and word recognition in the auditory ventral stream. PNAS, published online before print, February 1, 2012. doi:10.1073/pnas.1113427109

Liu, S., Seidlitz, J., Blumenthal, J. D., Clasen, L. S., & Razhahan, A. (2020). Intergrative structural, functional, and transcriptomic analyses of sex-biased brain organization in humans. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.1919091117

Rauschecker, J. P., & Scott, S. K. (2009). Maps and streams in the auditory cortex: Nonhuman primates illuminate human speech processing. Nature Neuroscience, 12(6), 718-724. doi: 10.1038/nn.2331

Rennels, J. L., & Cummings, A. J. (2013). Sex differences in facial scanning - Similarities and dissimilarities between infants and adults. International Journal of Behavioral Development, 37(2), 111-117.

Schmolesky, M. (2000). The primary visual cortex. Accessed February 2, 2005 from the Web site: http://webvision.med.utah.edu/VisualCortex.html

This page was first posted February 3, 2005