PSYC 380 Week 3 DB Forum 2 Example

Discussion Board Forum 2: Thread and Two Replies

PSYC 380 Physiological Psychology, Discussion Board Forum 2 (thread and two replies)

Thread by [Student Name]

The prompt and the classmates' posts are composites standing in for the course's own forum; the textbook and the two journal articles are real and described from their published sources; the requirements follow Liberty's public course guide for PSYC 380.

Thread

News stories regularly announce that scientists have found the part of the brain responsible for love, fear or faith, usually with a brain image showing a few bright patches. Carlson (2014) explains what lies behind those images. Functional MRI detects changes in the ratio of oxygenated to deoxygenated hemoglobin; when a region becomes more active, blood flow to it rises within a few seconds, and the scanner registers the change. The colors are statistical maps showing where that signal differed between conditions, not pictures of neurons firing. The response is also slow, peaking several seconds after the neural event, so the method is better at showing where activity changed than exactly when.

Logothetis (2008), comparing the signal with electrical recordings in monkeys, argued that it reflects mainly the input to a region and its local processing, not the signals the region sends out. He also cautioned that because many regions take part in many functions, finding activity in one place does not identify a mental process, and that the method is best combined with other techniques.

A second problem is sample size. Button et al. (2013) analyzed 49 meta-analyses covering 730 primary studies. They estimated median statistical power at about 21%, which means a typical study had roughly a one-in-five chance of detecting a true effect of the size the meta-analysis reported. Low power does more than miss effects. When an underpowered study does reach significance, its estimate of the effect is likely to be inflated, and the result is less likely to be true. Brain imaging is expensive, so many scanning studies have tested only a dozen or two volunteers, exactly the conditions under which this problem is worst.

Classmates: what would you look for in a news story before believing that a scan has located a feeling?

Reply to Kendra

Kendra, you described a study in which the amygdala lit up when people viewed frightening faces and concluded that the amygdala is the brain's fear center. The finding is real, but the conclusion runs backward. Logothetis (2008) warned that activity in a region rarely identifies one mental state, because regions contribute to many processes. The amygdala also responds to surprising, novel and even rewarding stimuli, so its activity might reflect attention to anything important. Carlson (2014) notes that lesion studies offer a stronger test: if damage to the amygdala impairs fear learning, that supports a causal role in a way the scan alone cannot.

Reply to Owen

Owen, I agree that lesion studies can test causation more directly than imaging, since removing or damaging a region shows what the brain cannot do without it. Carlson (2014) describes how such experiments in animals, along with human cases of brain injury, built much of what the field knows. Still, lesions have their own problems. Human injuries rarely respect the boundaries of a single structure, and the brain can reorganize after damage. Button et al. (2013) would also remind us that small samples affect every method, and many lesion studies involve few patients. Perhaps the strongest conclusions come when imaging, lesion and stimulation methods point in the same direction.

References

Button, K. S., Ioannidis, J. P. A., Mokrysz, C., Nosek, B. A., Flint, J., Robinson, E. S. J., & Munafò, M. R. (2013). Power failure: Why small sample size undermines the reliability of neuroscience. Nature Reviews Neuroscience, 14(5), 365-376. https://doi.org/10.1038/nrn3475

Carlson, N. R. (2014). Foundations of behavioral neuroscience (9th ed.). Pearson.

Logothetis, N. K. (2008). What we can do and what we cannot do with fMRI. Nature, 453(7197), 869-878. https://doi.org/10.1038/nature06976