The effect of age on the responses of the brain to decapitation (complete ischemia) was tested in the awake and anesthetized rat. The metabolic and reflected light activities were evaluated by the use of a DC fluorometer/reflectometer (one or two hemispheres), and the electrical activity was measured by electrocorticogram. In all 81 animals used in these experiments, the above-mentioned parameters were measured to enable comparison between the age groups. The rats were divided into six age groups ranging from 2 to 120 weeks, and each age group was subdivided into awake and anesthetized animals. The results can be summarized as follows. (1) The rate of energy consumption was lower in the young (2 weeks) and the old rats (120 weeks) compared to the adult rats. (2) The effect of anesthetic was more pronounced in the young and the old rats than in the adult rats. (3) The electrical activity was in good correlation with the energy availability in all animals of various ages as well as in the awake and anesthetized rats. Severe head injury can result in a high mortality rate or irreversible brain damage. One technique used to induce traumatic brain injury (TBI) is exposure of the brain to fluid percussion pressure while monitoring the increase in intracranial pressure (ICP). Since brain injury is a multifactorial, pathological, time-dependent state, the multiparametric monitoring approach was adopted for studying fluid percussion effects on the rat brain. A multiprobe assembly (MPA) connected to the brain in vivo (right hemisphere) enabled the simultaneous monitoring of CBF, NADH redox state, extracellular K+, Ca2+, H+ levels as well as DC potential, ECoG and ICP. The animal was connected to the monitoring system and exposed to TBI after a recuperation period of at least 3 h after the end of the operation. Two typical responses to TBI were recorded in our preliminary experiments. When severe injury was induced, ischemic depolarization (ID) developed, whereas mild or moderate injury led to repetitive spreading depression (SD) cycles. The relationship between the ID and SD observed under TBI is important to the understanding of the mechanism of brain injury. ICP before injury was between 2 and 6 mm Hg and increased to 20–22 mm Hg 2–3 min after the ID. After severe head injury, ICP remained high and in some cases increased to critical values causing death of these animals. Some animals developed seizures at various stages after the TBI. Hyperbaric oxygenation was used as a therapeutic tool to treat severely injured animals.