The Chemical Factory Inside Your Head

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How does your brain work? What causes proper brain function? What happens when the brain malfunctions? Research into the workings of this machinery is essential for unraveling the very principles of brain function, for understanding the mechanisms of major brain disorders, for developing effective medications to treat these disorders, and in the future perhaps even for enhancing the functions of the normal brain.

The brain contains complex biochemical machinery. The proper operation of this machinery is at the heart of proper brain function. The breakdown of this machinery — and there are numerous ways in which this breakdown may occur — is among the major causes of brain dysfunction.

The workings of the brain’s biochemical machinery impact virtually every process occurring in the brain — how the neurons communicate and exchange information; how the arousal necessary for the proper function of the brain is maintained; how attention is selectively deployed and sustained over time; how memories are formed and stored; and myriad other functions.

What We Know About the Brain

Signaling between neurons relies on chemicals known as neurotransmitters and neuromodulators. These chemicals are stored in tiny vesicles at the terminals where the neuron makes contact with other neurons, the synapse. An electric potential generated within the body of the neuron causes the neurotransmitters to be released from the presynaptic vesicles, to cross a microscopic space between the signaling and the receiving neurons, and to attach themselves to postsynaptic receptors found on the microscopic protrusions of the receiving neuron, the dendrites.

Numerous neurotransmitters and neuromodulators exist in the brain. They serve a variety of functions, which are not always easy to specify in terms of everyday language. The term “neurotransmitter” refers to a group of chemicals in charge of rapid communication and information exchange among adjacent neurons within local “neighborhoods” in the brain.

By contrast, the term “neuromodulator” refers to chemicals which act more slowly and exert their influence across distant brain regions. Glutamate and GABA are among the most ubiquitous neurotransmitters, the former mediating by and large excitatory signaling, and the latter mediating inhibitory signaling between neurons. Glutamate and GABA operate in synergistic tandem, and the balance between them is important for proper information processing and for brain health. The breakdown of such balance has been implicated in certain forms of seizure disorder and in neuronal atrophy.

Norepinephrine, dopamine, acetylcholine, and serotonin are among the most extensively studied neuromodulators. They exert their influence from various nuclei within the brain stem, from where they project into far removed regions of the brain. Norepinephrine is critical for maintaining arousal and activation throughout diverse brain regions.

By contrast, dopamine is important for signaling the salience of certain inputs, signifying their relevance to, and importance for, the organism’s needs and desires. Dopamine is sometimes refers to as the “reward” or “pleasure” neuromodulator. Several dopamine systems exist in the brain, and some of them have been shown to be severely impacted in addictions of various kinds. Dopamine may also be important for the formation of long-term memories.

Dopamine signaling is especially prominent in the frontal lobes and in the striatum, which are the brain regions particularly closely involved in organizing complex behaviors: in the amygdala, which is important in emotions; and in the hippocampus, which is important for memory formation. Some evidence exists that these two neuromodulators are somewhat unevenly represented in the two hemispheres.

According to these findings, norepinephrine is somewhat more prevalent in the right hemisphere than in the left hemisphere, and the reverse is true for dopamine. This asymmetry may have interesting implications for hemispheric specialization not only in humans but in a wide range of mammalian species.

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A magazine dedicated to the brain.

We believe that neuroscience is the next great scientific frontier, and that advances in understanding the nature of the brain, consciousness, behavior, and health will transform human life in this century.

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