Glia and the Other Brain
Having proved the neuron theory correct, Santiago Ramon y Cajal (1852-1934) set neuroscience on a definite path for understanding mental life. It would be a longterm project, but for Cajal, the secret of the mind lays in neural signaling. This has been the assumption until recently. However, neuroscience could have taken a different path. Cajal observed a whole class of other brain cells—glial cells—and took great interest in them. He thought they modulated neural communication and thereby were involved in both sleep and wake cycles and in attention (Garcia-Marin et al. 2007). However, glia don’t signal electrically and they lack action potentials. For someone interested in the chemistry of the mind, they didn’t seem relevant. The word “glia” is Greek for “glue,” and they were originally thought of as keeping neurons together. Neurons depend on glia for metabolic needs, detoxification, cleaning neurotransmitters from the synaptic cleft, and defense against foreign microbes. But glia also provide modulatory influence over neural communication and interconnect among themselves and with neurons through diffusing chemicals in intercellular space. While neurons communicate in a matter of milliseconds, glia communicate in seconds or minutes. It is becoming clear that glia are part of the chemistry of the mind and constitute a largely unanalyzed dimension of biopsychology.