ABSTRACT
Because the human brain is so metabolically active, it is exquisitely vulnerable to any toxic chemical that causes depressed metabolic activity. There are good reasons that psychiatrists and family physicians dealing with psychiatric patients should be focusing on toxic exposures. Although many of the organs in the human body are subject to environmental toxic chemicals, the human brain and the brains of marine mammals such as whales and dolphins are especially vulnerable. These large animals have larger physical brains in absolute terms, but when measured using the brain-tobody-weight ratio (which compensates for body size), the human ratio is almost twice as large as the ratio of the bottlenose dolphin, and three times as large as the ratio of a chimpanzee. Therefore, the brain is a very vulnerable target in humans and large marine mammals because of its large size compared to total body weight and its high concentrations of fats (including cholesterol and unsaturated essential fatty acids) present in myelin and neuron cell membranes.1 Many fat-soluble environmental chemicals deposit readily into this fatty tissue. Due to the fact that the brain is an extremely metabolically active organ (generating high quantities of free radicals), any amount of toxic chemical exposure only further increases the production of free radicals beyond baseline levels, quickly causing oxidative damage to the unsaturated fatty acids so important to brain function. The brain consumes up to 20% of the energy used by the human body, more than any other organ. Although the human brain represents only 2% of the body weight, it receives 15% of the cardiac output, consumes 20% of total body oxygen, and utilizes 25% of total body glucose.
