The Mid-Brain: Your Auto-Pilot

From the basal region, nerve channels branch out to the mid-brain region, which has a set of secondary control systems. Scientists also refer to this collection of structures as the limbic system. The mid-brain area produces various hormones, or “messenger molecules.” These include such hormones as the pituitary gland’s growth hormone and activating chemicals that cause your adrenal glands to secrete the excitatory hormone familiarly known as adrenalin. Other structures stimulate your thyroid gland to secrete thyroxin, which controls the overall pace of your body’s cellular combustion processes, better known as your metabolism. The pituitary, or hypophysis, is a busy little gland. About the size of a pea, it sits in its own private chamber, a small cavity hollowed into the bony brainpan, just above the roof of your mouth. Even this tiny brain structure is further divided fore-and-aft into two lobes, an anterior lobe and a posterior lobe. Operating largely under the supervision of the hypothalamus, the pituitary helps to regulate blood pressure; water retention; thyroid gland function; certain aspects of sexual function; aspects of pregnancy, childbirth, and lactation; overall body growth and size; and the conversion of food into energy. Other components in this limbic or mid-brain system include your thalamus, which serves as the central collection point for almost all sensory data going up to your cortex.The single exception to this thalamic centralization of data is the olfactory data, or the sense of smell, which goes directly to its own processing center in the cortex. The sense of smell is so ancient, evolutionarily speaking, that the olfactory nerves pass upward from the sinuses, through the cribiform plate—the floor of the brainpan—and into the olfactory bulb, a sensory sub-computer that sends its data directly to a special processing area of the cortex. The hypothalamus mediates arousal and emotion (and supervises the pituitary).The hippocampus plays a part in transforming short term memory into long-term memory. A nearby structure, the amygdala, serves as an early warning sensor, detecting patterns in the incoming stream of sensory data that might imply threats to your survival or well-being. Many neuroscientists believe that this constellation of structures in the limbic system, probably coordinated by the hypothalamus, plays a part in psychosomatic illness and psychosomatic healing. By some yet undiscovered process, it seems that the hypothalamus and its partners transform our various levels of conscious and non-conscious ideation into direct physiological consequences, as we’ll explore in more detail in a later chapter. As we’ll learn further, the developing field of psychoneuroimmunology seeks to understand the causative connections between conscious mental activity and immune function, as mediated through these primitive, non-conscious processes.