Responses to Oddballs: A Robust Finding in Neuroscience

When the brain encounters unexpected stimuli, it increases its activity.

Posted Jul 22, 2009

My first post invited readers to suggest a new metaphor for the human brain. I challenged you to come up with a metaphor that's superior to the computer metaphor. The computer metaphor, as employed by many psychological researchers, has encouraged a cold, cognitive conception of the brain, a paradigm that largely ignores emotion and motivation.

The metaphors that were suggested by readers are more biological than either the computer or my suggested metaphor, the car. One reader suggested the rat, which has been a classic model for humans in medical and psychological research. The rat could easily serve as a model mini-human. Its behaviors are driven by biological needs and drives: food, sex, and dominance, as examples. It makes perfect sense that our brains are built on the same basic structures as simpler mammals', but with more elaboration and greater complexity.

A reader proposed the metaphor of an ant colony, and another proposed a human city. These metaphors are intriguing because they suggest the possibility that the components function semi-independently. The humans in a city fulfill many different functions in order to keep the system operational, without necessarily being aware of what the others are doing.

Today, I'd like to write about some of the ways in which neuroscience research undermines the computer metaphor. One of the most robust findings in neuroscience research is increased brain activity to the unexpected. This finding would not be predicted by a cold, information-processing conception of how the brain functions.

What happens when a computer encounters something unexpected? Usually the computer program shuts down. Computer programs are created to deal with expected data, not unexpected data. When unexpected data is encountered, the computer is likely to stop processing.

When the human brain encounters unexpected stimuli, however, it increases processing. Human brains seem to recognize that unexpected stimuli are likely to be important.

This phenomenon is seen in research using event-related potentials. Event-related potentials (ERPs) are extremely fast electrical responses measured using electroencephalography (brain waves).

The research that shows the unexpected causes increased brain activity is conducted using an "odd-ball paradigm." The odd-ball paradigm has (in my opinion) the coolest name in psychological research, but unfortunately it is not quite as exciting as you might hope. The participant is exposed to a repeated stimulus, for example, a tone. The tone is repeated (beep, beep, beep, beep). At unpredictable intervals, the beep is replaced by a different tone (boop). The unexpected tone, the "boop," is the oddball. Oddballs cause a large response a component of the ERP called the P300. The P300 is a response that occurs about 300 milliseconds after the onset of a stimulus, and this "oddball" effect has been conceptually replicated using more complex stimuli like attitudinal issues.

A similarly large ERP occurs in mismatch negativity paradigms that use simple visual or auditory stimuli and these responses are seen as early as 150 milliseconds after the onset of the odd stimulus. Other neuroscience research has revealed that the anterior cingulate cortex (ACC) is so sensitive to deviations that some researchers joke that placing participants in the fMRI scanner causes ACC activity. These strong and reliable responses to the unexpected may underlie the experience of cognitive dissonance.

The fact that the human brain shows such a fast and reliable response to unexpected stimuli would not be predicted by a computer model of the brain. It would be predicted by a model of the brain in which motivation is primary, however. Unexpected stimuli are likely to be motivationally significant, likely to require action.