Watching the brain switch off ’self’

The researchers–led by Rafael Malach and Ilan Goldberg of the Weizmann Institute of Science reporting in the April 20, 2006, issue of Neuron–say their findings show that self-related function actually shuts down during such intense sensory tasks. Thus, an “observer” function in the brain does not appear to play an active part of in the production of our vivid sensory experiences. These findings go against common models of sensory experience that assume that there is some kind of “homunculus”, or observer function in the brain that “looks at” sensory brain areas. Thus the finding, they said, has significance for understanding the basic nature of consciousness and perception.

The experimental challenge that the researchers faced was to design one task that could be used to activate specifically either sensory processing or introspection brain areas. Their solution was to ask subjects to look at the same pictures or listen to the same musical phrases, but to perform two different kinds of processing on them. To explore sensory processing, the researchers asked the subjects to use buttons to classify the images as animal/non-animal, or the musical passages as trumpet/non-trumpet. And to study introspection, the researchers asked the subjects to indicate whether emotionally they felt strongly or neutrally about the image or musical passage.

During the tests, the researchers scanned the volunteers’ brains using functional magnetic resonance imaging. In this widely used technique, harmless magnetic fields and radio waves are used to scan blood flow in brain regions, which indicates activity.

The researchers found that regions of the brain activated during sensory processing or self-reflective introspection were quite distinct and segregated. Sensory processing activated the sensory cortex and related structures, while introspection activated the prefrontal cortex, they found.

Importantly, the researchers found that activity in the self-related prefrontal cortex was silenced during intense sensory processing.

As a result, wrote the researchers, “We propose that the role of self-related cortex is not in enabling perceptual awareness, but rather in allowing the individual to reflect upon sensory experiences, to judge their possible significance to the self, and, not less importantly for consciousness research, to allow the individual to report about the occurrence of his or her sensory experience to the outside world.

“To conclude, the picture that emerges from the present results is that, during intense perceptual engagement, all neuronal resources are focused on sensory cortex, and the distracting self-related cortex is inactive. Thus, the term “losing yourself” receives here a clear neuronal correlate. This theme has a tantalizing echoing in Eastern philosophies such as Zen teachings, which emphasize the need to enter into a ’mindless,’ selfless mental state to achieve a true sense of reality,” they wrote.