The second chapter in the present book on the brain is on cerebral hemispheric specialization and the associated topic of behavioral lateralization. As with other areas of brain study, the concept of networks is making inroads in this area. The findings in this regard reinforce the left hemisphere as differentially specialized for its skills relative to the right. Although each hemisphere has its specializations, the left hemisphere has been called dominant and, in this regard, the network approach is touting its efficiency and also its more centrally organized characteristics. Moreover, the findings show that even neonates possess this type of left-hemisphere specialization. These findings on the differential networking in the hemispheres are consistent with the present model that the left hemisphere possesses better activation–inhibition coordination skills compared to the right hemisphere, which has other inhibitory skills.
Aspects of manual behavior reflect the differential skills of the left and right hemispheres, and so reflect a manual specialization that reflects its underlying hemispheric specialization. Handedness is not as clearly related to hemispheric specialization as are other manual behaviors. Most often, language abilities are associated with the left hemisphere, which is why it is called the dominant hemisphere, but each hemisphere has its skill set (e.g., certain spatial skills in the right hemisphere) and, moreover, the advantages that each hemisphere possesses are relative rather than absolute ones. Research is showing that the left hemisphere is associated with certain cognitive skills, as well. The hemispheres work in concert in adaptation to context, problem-solving, and so on. Interhemispheric communication is important in this regard.
As for how the chapter is organized as it reviews the research on hemispheric specialization, manual specialization, and behavioral lateralities, and their relationship to handedness, language development, cognitive achievement, and so on, it considers each age period separately from preconception into childhood, in particular. For each age period under review, first, results of research related to manual lateralities are presented. Then, for each age period, other results related to the brain are presented. Finally, aside from considering the developmental origins of specialization/lateralization, the chapter considers evolutionary ones.