Schizophrenics often speak in a rambling, incoherent fashion, a symptom once considered evidence of demonic possession. Now researchers are investigating a less supernatural explanation. The problem, they say, may reflect a deficit in short-term memory.
Short-term, or working, memory is where we store the local pizzeria's telephone number between the time we look it up and the time we dial the phone. Most of us can store about seven bits of information for up to a minute before it slips away.
But recent studies have shown that the prefrontal cortex, where working memory resides, is significantly less active in schizophrenics. Since their memory circuitry is partially out of order, they may be unable to recall what they were thinking a moment earlier.
"If they cannot keep the subject of a sentence in mind by the time they get to the verb or object, it's going to be fragmented and incoherent," says Yale neuroscientist Patricia Goldman-Rakic, Ph.D.
The short-term memory theory might explain why drugs that reduce a schizophrenic's hallucinations do little to make his thoughts more coherent. Most of the drugs block a specific receptor--called D2--to the neurotransmitter dopamine. But the prefrontal cortex is richer in D1 molecules, which the drugs ignore.