A new Yale study has located the part of the brain active when humans imagine hearing things.
As part of a larger effort to understand the neural basis of hallucinations, researchers used fMRI imaging to observe brain activity when subjects both heard words or imagined the same voice saying them.
Two regions near the front of the brain activated differently for words the subjects judged as either heard or imagined. The finding has implications for understanding clinical conditions like schizoprenia that are characterized by such hallucinations, study co-author and Yale professor of psychology Marcia Johnson, in a Sunday said in an email.
“Auditory information is interesting not only for generality and because much of our social experience involves speech, but also because auditory hallucinations can be clincally significant,” Johnson said.
To investigate how the brain responds to heard as opposed to imagined words, the researchers first scanned the brains of subjects while they were being played real speech or while they imagined the words being spoken. The researchers later asked the subjects to recall whether the words were heard or imagined.
The results showed that the left middle frontal gyrus — a brain area involved in higher order cognition — was more active for imagined words correctly recalled as being imagined rather than heard, while the left inferior frontal gyrus — a region associated with processing meaning — activated more strongly for words subjects recalled as heard, whether or not the word had originally been heard or imagined.
According to Erich Greene, study co-author and data analyst working with Johnson, the takeaway from this study is that human beings are not as good at remembering what they heard as they think they might be. The study shows that, as human beings, we have a limited amount of attention and processing power, Greene said.
He added that, in general, human tendencies to imagine things often arise from their expectations. For instance, Greene said, memory of whether a Republican or a Democrat said something comes from our inherent biases based on what we already know about Republicans and Democrats.
“Our judgments don’t come out of nowhere,” Greene said. “They’re not perfect but even when they are imperfect, we have traces that lend themselves to specific misinterpretations.”
Johnson said the research team would like to replicate and extend the finding to better understand the neural mechanisms of imagined and heard words. In the current study, subjects were only scanned while hearing or imagining words, not while they recalled the experience of hearing or imagining, and Johnson said she would like to extend the scanning session to this final component as well.
The study was published online in the journal Psychological Science on Jan. 17.