Does the brain have a center of consciousness? Until now, the prevailing opinion has been that anesthetics and other agents of unconsciousness act widely across the cerebral cortex and spinal cord. But a new finding suggests the existence of a barbiturate-sensitive switch (M. Devor, et al., "Reversible analgesia, atonia, and loss of consciousness on bilateral intracerebral microinjection of pentobarbital," Pain, 94:101-12, October 2001). Using barbiturate microinjections, Hebrew University of Jerusalem researchers surveyed most of the subcortical forebrain, midbrain, and hindbrain of rats. An anesthesia-like state was induced when the drugs were administered to a small, football-shaped area in the upper brainstem's reticular formation that they dubbed the mesopontine tegmentum anesthesia locus (MPTA). "I'm not sure that the MPTA can be represented as a 'center' of consciousness in the sense that its neurons run an algorithm that manifests awareness," warns biology professor and coauthor Marshall Devor. "I prefer to think of it as an experimental lead, the 'end of a rope' that could lead us to the circuit that runs this algorithm." His group plans to lesion the MPTA and stimulate it with regionally applied anesthetics rather than microinjections. "To what extent does the MPTA act synergistically with other brain areas [such as] the spinal cord?" Devor wants to know. Ultimately, he thinks it might be possible and safe to manipulate the zone to help bring patients out of coma. "These are early days," he reflects, "just the beginning of research on systems anesthesiology."
Estrogen Aids Cognition in Post-Menopausal Women
Estrogen replacement can benefit the cognitive abilities of post-menopausal women, but the effect does not appear to be great, according to a review of some 70 brain neuroimaging studies of estrogen replacement (Y.R. Smith, et al., "Neuroimaging of aging and estrogen effects on central nervous system physiology," Fertility and Sterility, 76:651-9, October 2001). "The literature we have so far about estrogen and cognition seems to point towards some benefit, although it's really not well defined in terms of what areas of neuropsychological testing it's going to be in," says Yolanda Smith, assistant professor of obstetrics and gynecology at the University of Michigan. "Is it verbal memory versus spatial memory versus attention? The different papers ... have different results about which areas. But the majority do point to women having some improvement in the women that are on estrogen." Smith notes studies demonstrate that estrogen increases cerebral blood flow and does decrease damage in the brain's white matter-structures such as axons. Decreasing damage in white matter, she says, means that estrogen may decrease circulatory damage. While Smith, along with a number of other researchers, says it's premature to prescribe estrogen for its impact on mental function, the findings so far on brain physiology do show that "being on a hormone can change what's happening in your brain, and points to [its] plasticity."
