Resting states in unconscious monkeys

Nature has an interesting report from Marc Raichle‘s laboratory that studies the resting states in monkeys. This study not only demonstrates that resting states occur in non-human primates, but that it is possible to find such activity during unconscious states.

The authors found three separate networks showing organized patterns of activity in anaesthetized monkeys. These systems also display spontaneous BOLD signal fluctuations in awake humans. First, they investigated the oculomotor system and found spatially and temporally robust activity in discreet areas of this system. Second, the authors found similar spontaneous BOLD signal fluctuations in regions of the somatomotor system, which is involved in movement and touch.  A third network of spontaneous activity was found in the visual system.

The findings raise the question of whether similar findings can be made in unconscious humans. If this is the case, the activity clearly does not reflect conscious thought, and it may signal a more basic aspect of functional organization of the brain that may be conserved throughout animal evolution.

Intrinsic functional architecture in the anaesthetized monkey brain.

Vincent JL, Patel GH, Fox MD, Snyder AZ, Baker JT, Van Essen DC, Zempel JM, Snyder LH, Corbetta M, Raichle ME
Nature. 2007 May 3; 447(7140): 83-6

The traditional approach to studying brain function is to measure physiological responses to controlled sensory, motor and cognitive paradigms. However, most of the brain’s energy consumption is devoted to ongoing metabolic activity not clearly associated with any particular stimulus or behaviour. Functional magnetic resonance imaging studies in humans aimed at understanding this ongoing activity have shown that spontaneous fluctuations of the blood-oxygen-level-dependent signal occur continuously in the resting state. In humans, these fluctuations are temporally coherent within widely distributed cortical systems that recapitulate the functional architecture of responses evoked by experimentally administered tasks. Here, we show that the same phenomenon is present in anaesthetized monkeys even at anaesthetic levels known to induce profound loss of consciousness. We specifically demonstrate coherent spontaneous fluctuations within three well known systems (oculomotor, somatomotor and visual) and the ‘default’ system, a set of brain regions thought by some to support uniquely human capabilities. Our results indicate that coherent system fluctuations probably reflect an evolutionarily conserved aspect of brain functional organization that transcends levels of consciousness.