In my opinion, the evidence, scientific as well as textual, weighs heavily against the cardiac theory.
On the textual side, even Narada Thera, in The Buddha and His Teachings, admits that: "In the Patthana, the Book of Relations, the Buddha refers to the seat of consciousness, in such indirect terms as "yam rupam nissaya—depending on that material thing", without positively asserting whether that rupa was either the heart (hadaya) or the brain. But, according to the view of commentators like Venerable Buddhaghosa and Anuruddha, the seat of consciousness is definitely the heart. It should be understood that the Buddha neither accepted nor rejected the popular cardiac theory" (425).
Should we then favor Buddhaghosa over the evidence? I say no. It is often stated as a fact that the seat of consciousness is the heart or heart-base; nevertheless, the Buddha never explicitly states this and an increasing amount of scientific evidence is suggesting otherwise. Therefore, I would say that the cardiac theory, as much as people try to defend it with textual references and logic, is looking less and less tenable if we look solely at evidence at hand. Perhaps there is a means by which the two perspectives can be reconciled; however, I have yet to see one that sufficiently does so.
Neuroscience, on the other hand, has provided evidence that consciousness is centered in the brain.
There is, for example, data on the correlations between brain events and conscious experiences. Then there things such as the experiment done on the way the brain codes and recodes visual stimuli that effectively showed how one can "... even 'inject' such experiences into the brains of experimental animals, as demonstrated, for example, in elegant experiments () in which monkeys responded (behaviourally) to microstimulation of a circuit encoding a particular direction of motion in the same way that they had been trained to respond to an exteroceptive stimulus having the same directional value" (Gray, ).
Another example that I find rather interesting are the results of so-called brain bisection operations, which I suppose can be interpreted as showing nothing more than the experience of consciousness being processed and recognized in the brain, but can also be interpreted as supporting the theory that consciousness is centered in, or even the product of, the two hemispheres of the brain operating together ().
While far from being conclusive, scientific data certainly lends this theory considerable credibility.
"Sabbe dhamma nalam abhinivesaya" ().
(non-Buddhist related blog)