Friday, February 24, 2012

The Claustrum

"The brain science of bizarre behavior. If someone wants to, say, amputate his perfectly healthy arm, the call goes out to V.S. Ramachandran"

"I'm mainly an experimental scientist and we go with the flow. It's like charting the source of the Nile. You don't know when the next surprising twist and turn is going to be. It's a great adventure. A grand love affair with nature with all these twists and turns and unpredictable events. That's how we do experiments, but all of it is headed towards the goal of understanding human nature, but understanding it piecemeal. For example, you can't ask, "What is consciousness?" Some people do, but it's too nebulous an idea. In fact, philosophers have criticized this approach. But I think it's okay to ask question like Francis Crick did.
Well, what is consciousness? Philosophers like Colin McGinn and others have argued that this is utterly mysterious. The human brain can never comprehend itself and certainly not comprehend mysterious phenomenon like consciousness. Somebody like Crick would vehemently disagree. And I would agree with Crick.

Crick and Koch, for example, have argued that there is a structure called the claustrum that is a thin layer of tissue underlying the insular cortex of the brain. What's exciting about this layer of tissue, what caught Crick's eye and Koch's eye, was that it doesn't have any known function unlike other regions of the brain. There are many regions that we don't know the function of, but the claustrum is especially mysterious. It's not a tiny, little structure. It's a medium sized structure, and it's homogenous in its cell constituents. It also doesn't have the layered structure as with the rest of the cortex.

The astonishing thing that Crick noticed was it's connected to almost every part of the brain including every part of the cortex. It seems reciprocal. It sends connections to the somatic sensory cortex and receives connections back from the somatic sensory cortex. It sends signals to the amygdala, back from the amygdala, to the anterior cigulate, back from the anterior cigulate. In fact, it's very hard to find any region of the brain that is not connected to the claustrum. John Smythies, in our lab, and I have now picked up the gauntlet where he left it.

Crick, for example, has been rewarded in the past for analogies, for big metaphorical leaps. I don't think he actually says this, but if you look at the double helix and the complementarity of the helix, the two sides of the helix, we're struck by the analogy between this and the complementarity between parent and offspring. There's a huge leap of faith there. He says why do dogs give birth to dogs and not to pigs? Any child will ask this question, you and I won't. But Crick asks that question—why do dogs give birth to dogs and not to pigs? There's a complementarity between offspring and parent. Might it be the case that the complementarity of the two strands of the helix actually dictates complementarity of offspring and parents? This was the big leap. Then, of course, he figured out the genetic code and modern biology was born. He's primed to think in terms of linking seemingly unrelated phenomenon, of linking structure and function.
Then he approaches the claustrum and he says, What's the most fundamental thing about consciousness? So axiomatic, in fact, that you take it for granted? That is the fact that you are one person; unity of many attributes of human consciousness. The continuity. The time travel—the ability to go to and from in time—looking into the future, visit nostalgic memories from the past, string them together in approximately the right sequence. Laughter is uniquely human and we can't imagine laughing without being conscious, many attributes of human conscious experience. Self-awareness is another attribute. Putting it crudely consciousness is aware of itself.

Now, the central attribute of human conscious experience, so fundamental, in fact, that we take it for granted, don't pause to think about it, is the sense of unity. You've got a diversity of sensory experiences. You see things, you listen to things. This harks back to what I was saying about synesthesia. You taste things. You have hundreds of memories throughout a lifetime. Yet you think of yourself as a unified person. Yet all of these happen to you. You, John, or me, Rama. It all happened to me and I'm one person. Despite this diversity of sensory experiences, this bewildering sensory cognitive blitz of memories and sensory impressions I experience unity. How does that come about?

Another way to formulate this question is that there are different brain regions actively processing different aspects of information including memories and yet you experience yourself as a unity. Many philosophers will argue this is a pseudo problem, not a true problem. In fact, Crick adopts the opposite view; he and Koch debunk the idea that it's a pseudo problem. He says the most axiomatic thing about consciousness is its unity. And guess what the claustrum is doing? It's getting sensory inputs, even inputs from the motor cortex. It's getting inputs from every region of the brain in one little gathering place and sending messages back. It's ideally suited for performing this unifying role.

There's an analogy here between what the structure of the claustrum is and what the phenomenology of consciousness is. Maybe this is not just a superficial analogy. Maybe it's deep. Maybe the clue to consciousness lies in looking at the structure of the claustrum, a detailed study of its microanatomy and its connections to the rest of the brain.

Questions of that nature, trying to explain functions like consciousness, like self-awareness, like qualia, in terms of brain structures, is something that Crick pursued, and I think its something that I'd like to pursue as well, and we have been trying. We all share his agenda—though obviously not his stature. "

Read more:     Adventures in Behavioral Neurology