Neuropalooza, day two.
Some fascinating presentations this afternoon on corollary discharge. Corollary discharge is the brain’s mechanism for distinguishing between self-generated and external stimuli. It helps the brain disregard sensations that are generated by our bodies own movements. For instance, when we view a painting, our eyes are constantly moving across it. Yet, the painting appears stable. For that, we can thank corollary discharge—the messages the brain’s motor centers send the sensory processing areas, warning them about upcoming movements. These messages allow the sensory centers to anticipate the sensory ramifications of the body’s movements and essentially tune them out. (One of today’s speakers provided the following brilliant analogy for corollary discharge: It’s as if the motor cortex is sending the body an e-mail telling it how to move and cc-ing the sensory cortex to keep it apprised of impending movements.)
In any case, today’s symposium had two highlights. The first was a presentation by Berthold Hedwig, who studied corollary discharge in the auditory systems of crickets. In order to attract mates, male crickets rub their wings together, generating loud songs. The songs are so loud, in fact, that the males, who are forced to listen to their own songs continuously, should be deafened by them. But they’re not—thanks to corollary discharge. Scientists in Hedwig’s lab discovered that when a male cricket sings, his motor system sends a signal, via one specific type of neuron, to his auditory pathway. This signal inhibits the auditory neurons, reducing their response to the cricket’s own sound. Interestingly, they also found that these signals are generated even when a cricket engages in “silent singing”—which occurs when a male has one of his wings removed, rendering him unable to create sounds.
Turning now to corollary discharge in humans…Judith Ford spoke about her research on the role that corollary discharge dysfunction may play in schizophrenia. Since corollary discharge provides a way for the brain to distinguish between self-generated and external stimuli, it’s logical that disruptions of this system might be associated with the hallucinations and delusions associated with schizophrenia. Ford’s results support this notion. She measured brain activity in schizophrenics and non-schizophrenics as they spoke aloud. Schizophrenics showed significantly less evidence of corollary discharge—their motor systems did not seem to be preparing their auditory systems for the sounds they were about to speak. Such impairments could help explain schizophrenics’ inability to distinguish between the internal and external, and Ford is continuing to test and expand upon this intriguing idea.
My other favorite symposium of the day was the one on “the new neuroimmunology.” For years, many scientists thought that neurons were the only cells in the body that didn’t express appreciable amounts of immune system molecules. Now, we know that’s not true, and it looks as though proteins of the immune system have surprising, important, and unique roles in the brain. I’m too tired and jet-lagged to go into the details, but if you’re interested, you should check out the work of Carla Shatz, who is providing compelling evidence that immune proteins expressed by neurons influence synaptic plasticity, and Lisa Boulanger, who is studying whether the immune proteins expressed in the brain may play a role in disease, particularly autism and schizophrenia. Neuroimmunology seems sure to yield some important new insights in the years to come.
The conference isn’t even half over yet, so stay tuned.