The Handy Psychology Answer Book. Lisa J. Cohen

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      What does the hindbrain become?

      The hindbrain divides into the metencephalon and the myelencephalon. These two sections subsequently develop into the cerebellum and pons on one hand and the medulla oblongata on the other. The pons and medulla oblongata are both part of the brain stem. Together with the cerebellum, they form the reptilian brain of Paul MacLean’s triune model.

      What does the midbrain become?

      The midbrain divides into the tectum and the cerebral peduncle. These deep brain structures lie just above the brain stem. In primitive vertebrates such as amphibians, fish, and reptiles, the tectum serves as the main visual processing center in the brain. In primates, its function is more restricted as the majority of visual processing is done in the neocortex. The primate tectum helps to control eye movement. The cerebral peduncle includes several brain areas that contain the neurons that produce important neurotransmitters. For example, the substantia nigra is the origin of a major tract of dopamine neurons. We are now learning that the midbrain played a central role in the evolution of early emotional systems.

      What does the forebrain become?

      The forebrain develops into the evolutionarily newest parts of the brain and those most closely involved with complex mental life. The forebrain divides into the diencephalon and the telencephalon. In MacLean’s model, the forebrain includes both the paleomammalian and the neomammalian brains.

      What does the diencephalon turn into?

      The diencephalon divides into the thalamus, the hypothalamus, and several related regions. The thalamus is involved with sensation. It is the relay station between the sense organs and their corresponding cortical regions. Olfaction (smell) is the only sense modality that does not run through the thalamus as it is processed directly by the olfactory bulb. The hypothalamus links the brain to the autonomic nervous system and serves a critical role in emotion, connecting the mental aspects of emotion with the body’s physical response.

      What develops from the telencephalon?

      The telencephalon contains the most advanced parts of the brain. Although present in all vertebrates, it is most developed in birds and mammals. In humans the telencephalon develops into the cerebral cortex, the limbic system, the basal ganglia, and important white matter regions. The cerebral cortex includes the four lobes of the neocortex as well as those areas on the inside surface of the cortex that directly contact the subcortical regions. These include the cingulate gyrus, hippocampal, and parahippocampal regions, as well as the insula, which is sandwiched between the temporal, frontal, and parietal cortices. The basal ganglia, amygdala, and septum also develop out of the telencephalon. Finally, cerebral white matter is made up of bundles of axons that travel across large sections of the brain. Important cerebral white matter structures that develop out of the telencephalon include the anterior commissure, the internal capsule, and the corpus callosum.

      What does it mean to say that the brain is plastic?

      Plasticity of the brain refers to the brain’s ability to change with experience. As the very development of our brain is dependent upon our experience, we can say that the human brain is very plastic. In fact, brain development in humans is more experience-dependent than in any other species, reflecting the central role our capacity to learn has played in human evolution.

      What impact does brain injury have during fetal development?

      Because such extraordinarily complex structures develop out of very simple cell groupings, early problems in neuro-development can lead to severe birth defects. For example, spina bifida is linked to defects in the neural tube. In fact, serious problems in the first trimester of pregnancy often lead to miscarriage, such that 80 percent of miscarriages occur in the first trimester. When we consider the enormous lengths the brain must travel in its journey to maturity, it is indeed remarkable that so many human beings are born without brain damage.