Stimulating the central lateral thalamus produces consciousness

(Warning: neuroscience weeds)

The thalamus.
Image credit: Wikipedia

A couple of people have asked me about this study, described in numerous popular science articles (such as this one).  A monkey had electrodes installed in its brain that allowed scientists to stimulate parts of its thalamus, the region at the center of the brain which links the cortex to the brainstem and other systems, as well as serves as a relay station for some inter-cortical communication.

Stimulating the monkey, while it was anesthetized, in the central lateral thalamus region caused it to wake up, look around, and reach for things.  Ceasing the stimulation caused the monkey to immediately lose consciousness.  Notably, this region is heavily interconnected with frontal and parietal regions.

Diagram showing the various regions of the thalamus
Image credit: Madhero88 via Wikipedia

Interestingly, stimulating the medial dorsal thalamus, which is heavily connected to the prefrontal cortex, “proved less effective”, and stimulating the central medial thalamus, which projects to the striatum, was also less effective.

In other words, consciousness seemed to be associated with the central lateral thalamus region and its projections to layers in the frontoparietal network.

Diagram showing the regions of the brain
Lobes of the brain
Image credit: BruceBlaus via Wikipedia

One interesting point about this study, is it seems to contradict another study from a year or two ago which ruled out the thalamus as having a role in wakefulness (favoring the basal ganglia instead, if I recall correctly), a reminder that it’s not a good idea to hang too tightly on the results of individual studies.  Another point is the demonstration that the frontoparietal network overall, not just the prefrontal cortex, seemed to be most important for stimulating consciousness.

What does it all mean?  Well, it seems like a dramatic experiment.  And it seems to re-establish the role of the thalamus in wakefulness.  The part about stimulating the regions projecting to the prefrontal cortex not being effective makes me wonder about implications for higher order theories that focus on that region.

All that said, I think we have to bear in mind the distinction between the state of consciousness, that is wakefulness or vigilance, and awareness.  A lot of the information in this experiment seems to be about the state more than awareness.  In that sense, some of the anatomical details are new, but the overall macroscopic picture doesn’t seem to be much affected.

But this is a technical paper and there are probably implications I’m missing.  In particular, the implications for anesthesiology  and other clinical situations may be very significant.