LSAT 148, Section 2, RC Passage 4, Brain Scans

RC Passage 4 Explanation

Paragraph Summaries

1. Brain scans can be used in two ways: medical diagnoses, and for psychology. The first use is straightforward. The second relies on the assumption that the mind can be analyzed in separate modules. This is called the modular theory of mind.
2. But it’s possible that mental activity can’t be separated into modules, and nor can the physical processes that power mental activity. A psychologist says that mental processes are part of general mental activity distributed throughout the brain. For example, anger uses both emotion and reason.
3. If so, why do brain scans light up? It’s because brain scans are actually subtraction. If baseline mental activity everywhere in the brain is 100, and anger makes the amygdala light up to 120, then the picture will subtract 100 from all parts of the brain and just show the 20 in the amygdala. [This last sentence is my own example to clarify the situation. I’ve included it because that sort of understanding is definitely something I took from this paragraph.]
4. A problem with these images is that they hide the fact that the whole brain is active. It’s possible the striking fMRI images are what make the modular theory of mind attractive.

Analysis

I’m sure you’ve seen images of brain scans. One specific part of the brain is lit up. What this passage is telling us is that actually, the whole brain is lit up. But the section in question is lit up more. And to make a more vibrant image, the people producing the brain scans subtract away baseline brain activity, leaving only the extra activity in the specific area.

The passage has an unusual structure:

1. Brain scans for psychology depend on the modular theory of mind.
2. The modular theory may well be wrong.
3. How do we account for scan images? Well, they’re just subtraction.
4. Maybe the scans are part of what makes the theory popular.

I would say the point of the argument is to show that the modular theory of mind is probably wrong, and that the fMRI images supporting it are misleading.

One important note is that the subtractive images produced by fMRIs are not “how the brain looks”. Their use is a choice made by the psychology profession.

17-21 are important lines. They describe William Uttal’s theory that brain activity is part of a general mental process. The author agrees with this theory.

Lines 34-46 are also vital. There, the author describes what fMRI’s actually do, as opposed to what people think they do. People think fMRI’s only show the brain regions active during a mental state. But actually, all parts of the brain are active: the parts lit up in an fMRI are just the parts with the biggest change in activity.

So, for example, it’s true to say that the amygdala is the part of the brain most active during emotions. But the whole brain is active, and likely contributing to the state. This is the author’s main point. In the fourth paragraph the author shows that the modular theory of mind is based on this false impression given by subtractive method brain scans.

The modular theory of mind has one flaw the author likely believes, but doesn’t explicitly say: it’s possible for a brain region to be involved in an activity, even if that region doesn’t increase its activity during that time. So, if you’re feeling anger, your prefrontal cortex may be doing one thing. During sadness, it may do another thing. In neither case does it increase its overall activity level. But, by doing a different activity that takes the same amount of oxygen, that brain region is still contributing to the thought process.