Monday, February 20, 2006

A Profound Threshold

What is the most powerful computational device on the planet? If you answered "the human brain" you would have been right . . . until a few months ago.

As you may know, the brain is exquisitely designed to process information. Its array of 100 billion neurons, interconnected in a lattice of 100 trillion synapses (connections), is capable of processing an estimated 100 trillion pieces of information every second. This is an unfathomably large amount of computation.

When I took a computer class back in college in the 1980s, no man-made computer could even come close to that sort of processing capacity. Not even one millionth as much! It was impossible to believe that a computer could ever come close to rivaling our cerebral 'hardware'. But I remember one of my professors telling us to watch out for Moore's Law - which states that computer processing speeds double every 12 months or so. Due to inexorable technology advances, computers just keep on getting faster and more powerful, with no foreseeable end in sight.

As a result, the world crossed a remarkable threshold last year . . .

For the first time in history, the human brain was supplanted as the most powerful computer on earth. That distinction is now held by an IBM supercomputer known as Blue-Gene/L, which clocked in this past October at an astonishing 280 trillion operations per second. It has about three times more processing capacity than the human brain! (Sadly, it's being used by Livermore Laboratories to help develop our nuclear arsenal - your tax dollars at work.)

Does that mean that computers will soon be exhibiting superhuman intelligence? Well, in some ways, of course, they already are. Gary Kasparov, the best chess player in history, can no longer beat the best computer chess programs.

But it will still be many years before computers are able to accomplish several of the computational feats that we take for granted. The ability to understand and generate language looks like it will be the toughest 'artificial intelligence' problem - and computers at present are nowhere close to being able to do this. Mostly it's because artificial intelligence researchers and programmers usually don't have super-powerful computers at their disposal . . . most of them use the same desktop PCs that you and I do, which means they have less than 1/100,000th of the processing power of a human brain.

This will change in the decades ahead, however. Because of Moore's Law, it's fairly safe to assume that a good desktop PC in the year 2020 will have about the processing power of a human brain . . . enough to do a creditable job simulating human language.

While there is certainly much to be concerned about with such developments, in some future post I'll discuss some of the potentially positive implications regarding our understanding and treatment of mental illness.

Wednesday, February 15, 2006

Antidepressants in the Real World

First, kudos to ns, who was right on the money about the median length of time people stay on antidepressant medications (last week's 'challenge question'). According to a definitive study just published in the American Journal of Psychiatry, about half of all patients stop taking their meds within the first month.

This is a big problem, for a number of reasons:

(1) The vast majority of depressed patients will not achieve full recovery after just one month of treatment, and incomplete recovery is a huge risk factor for the recurrence of full-blown depression. Sadly, depression will return again eventually for 70-80% of all treated depressed patients - and that risk level actually goes up for those who terminate treatment before they're fully recovered.

(2) Because it's routine practice to prescribe antidepressants for at least 4-6 months (often much longer), it's safe to assume that most patients are discontinuing meds against medical advice. In other words, they're just stopping abruptly on their own. Unfortunately, most antidepressant meds have a well-defined withdrawal syndrome - which can include dizziness, nausea, headaches, lethargy, agitation, irritability, and even "electric" shock-like sensations in the head or limbs. Quitting these meds abruptly - without a doctor's supervision - can increase the chances of having these horrible withdrawal effects.

(3) The short-term 'cure rate' of antidepressants is low enough as it is - as low as 28% in the largest study published to date. And that's for the people who actually stay on the meds as prescribed . . . which means that the true cure rate in the real world is considerably lower, given how many patients discontinue treatment early.

But why would so many people stop taking their meds against the advice of their doctor? Although cost may be a factor in a small number of cases, in my clinical experience it's the nasty side effects that are usually the culprit. Sexual side effects - including an inability to experience orgasm and decreased libido - are quite common, especially in the SSRI class of meds that includes best-sellers like Zolft, Celexa, Lexapro, Prozac, and Paxil. Less talked about, but equally common, is the phenomeonon of 'emotional numbing' - a reduced intensity of negative emotions like sadness and anxiety, but also the blunting of positive emotions like joy and excitement (the movie Garden State did a nice job of portraying this phenemenon).

So, although they are truly a godsend for some, antidepressants don't represent a lasting cure for the majority of depressed individuals. Fortunately, there are other treatment options that look more promising for long-term success in the battle against depression, among them: aerobic exercise, omega-3 supplementation, behavioral activation, and interpersonal psychotherapy. I'll plan to elaborate on these in an upcoming post.

Thursday, February 09, 2006

Returning Soon With More Punditry

Dear Readers:

I'm afraid I got swamped again with academic deadlines over the past couple weeks, but will be back with timely posts and lots of fresh material in the days ahead.

Thanks for your patience!

In the meantime, a challenge question . . .

What is the average length of time a patient on antidepressants actually stays on their meds? [Hint: The answer is published in the January issue of American Journal of Psychiatry]