4.5: Measuring Behavior through Biology

Learning Objectives

1. Identify some biological measures that reflect thoughts or feelings.

This section briefly describes a few ways that biological measures, such as of measures of the brain, breathing and heart rate, or hormone levels, can be used in research on behavior.

Measuring the Brain

There are many ways to categorize the techniques that are used when studying the brain, but neuroscientists tend to differentiate between non-invasive techniques versus invasive techniques. As social science researchers, very few will use invasive techniques so they will not be discussed here. Instead, we cover some non-invasive techniques in which we are able to study the brain without getting direct physical access to the brain (think of fixing a broken pipe in a wall without having to open the wall up). Techniques have been developed that allow us to see what the brain looks like, as a still image (structurally) or in action (functionally). While not reviewed here, following ethical guidelines for both psychological and medical research should be followed when using physiological measures of thoughts, feelings, or behavior; these are sometime called psychobiological measures.

Structural Imaging

Structural imaging include a variety of tools that take pictures (images) of the physical features of the brain. These techniques are useful in many situations such as locating tumors, sites of physical brain damage, or finding size differences between the structures of the brain between various groups. Magnetic resonance imaging (MRI), for example, is one such technique that is commonly used to study the brain and to diagnosis knee and shoulder injuries. Structural imaging techniques allow us to look inside the brain (or body) without having to go inside.

Figure \(\PageIndex{1}\): An MRI (A structural image) of the brain. Note the ability to see specific gyri (bumps) and sulci (grooves).

A series of MRI images can be used to create a picture of the brain.

Functional Imaging

Many researchers are also interested in how the brain works. Some studies begin with the scientific question of “what does this part do?” Or more commonly, “Where in the brain does this happen?” Functional imaging techniques allow researchers to learn about the brain activity during various tasks by creating images based on the electrical activity or the absorption of various substances that occurs while a subject is engaging in a task. Such techniques can be used, for example, to visualize the parts of the brain that respond when we're exposed to stimuli that upset us or make us happy.

Figure \(\PageIndex{2}\): Functional MRI of a teenage brain conducting a working memory test. The regions in red and yellow, primarily in the frontal lobe and occipital lobe, are the most active.

Biological Chemicals

Another way to measure the brain is through neurotransmitters. Neurotransmitters one way that the brain communicates with itself and the rest of the nervous system. Table \(\PageIndex{1}\) (CC-BY OpenStax) shows a sampling of how the neurotransmitters may potentially affect behavior.

Table \(\PageIndex{1}\): Major Neurotransmitters and How They Affect Behavior (CC-BY OpenStax)

Neurotransmitter	Involved in	Potential Effect on Behavior
Acetylcholine	Muscle action, memory	Increased arousal, enhanced cognition
Beta-endorphin	Pain, pleasure	Decreased anxiety, decreased tension
Dopamine	Mood, sleep, learning	Increased pleasure, suppressed appetite
Gamma-aminobutyric acid (GABA)	Brain function, sleep	Decreased anxiety, decreased tension
Glutamate	Memory, learning	Increased learning, enhanced memory
Norepinephrine	Heart, intestines, alertness	Increased arousal, suppressed appetite
Serotonin	Mood, sleep	Modulated mood, suppressed appetite

In addition to brain chemistry, a more long-lasting way that chemicals affect behavior is through hormones. According to Williams Jones (2025), hormones can be measured as a way to chemically measure potential behaviors related to aggression, stress, bonding, or sexual behavior. For example, you could use a survey or interview to ask respondents how stressed they feel, or you could measure their levels of cortisol.

Additional Biological Measures of Behavior

Other typical psychobiological measures include pupil dilation, heart rate, blood pressure, galvanic skin response to measure mood. If galvanic skin response (GSR) is new to you, it's a measurement of how the sweat on your skin conducts electricity. All of these biological measures are affected by physiological arousal, such as when someone is upset or excited. If changes are shown in these measures to different stimuli, then we can assume that the stimulus affected mood somehow.

Advantages and Disadvantages of Psychobiological Measures

What do you think?

What do you think are some advantages of using psychobiological measurements to assess thoughts, feelings, or behaviors? What could be some disadvantages?

What benefits of using biological measurement to assess psychological phenomena did you come up with? One advantage of these types of measures is that they are objective, rather than self-report. Rather than have someone complete cognitive tests, we could see their brain's structure or ask them. Rather than ask which picture is preferred, the pictures can be shown while participants are in an fMRI to see what parts of their brain are most active.Rather than have someone fill out a self-report depression inventory, their dopamine and serotonin neurotransmitters could be measured.

What disadvantages did you think of? After reading this section, you may have noticed there is some inference involved in using biological measures to measure psychological concepts. We know that cortisol is related to stress, but there could be physiological or emotional reasons for the increase in cortisol and we can't know which. Is the person fighting an infection, or are they worrying about a future exam? Similarly, while there be a correlation between scores on certain cognitive test and structures in the brain, we don't know which came first. This is the classic "correlation versus causation" or "What about Z?" issue; maybe something caused both structural abnormalities and scores on the cognitive test (such as childhood malnutrition).

With just about everything related to designing a research study, it is up to the researcher to decide what is most appropriate for answering their research question, including how to measure the variables. As you read research articles, you should also be critically thinking about the choices that the researchers made; were their choices the best to answer their research question, or the maybe just the most convenient? Maybe psychobiological measures might be best, but MRIs are expensive and complex, so maybe a cognitive test was just simpler to use to complete the study. Or maybe we want to measure actual behavior, not correlates or proxies of behavior, so psychobiological measures aren't the best option. As you continue learning about designing studies, you'll see that there are many ways to collect data; you are encouraged to consider many options and decide on your own which option may be best for each research question.

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References

Williams Jones, E. (2025). Psychobiology: What is it and what does this science study? Psychology for Mental Health. https://psychologyfor.com/psychobiol...science-study/

Attributions

• Psychophysiological Methods in Neuroscience by Zachary Infantolino and Gregory A. Miller is licensed under a CC BY-NC-SA 4.0 International License.
• Figure \(\PageIndex{1}\): "Deadstar's brain" by Daniele Oberti is licensed under CC BY-NC-ND 2.0
• Figure \(\PageIndex{2}\): "fMRI Image of Preteen Brain" by NIH Image Gallery is licensed under CC BY-NC 2.0
• Table \(\PageIndex{1}\): Major Neurotransmitters and How They Affect Behavior by OpenStax licensed under CC-BY 4.0