Neuropsychological Constructs, Assumptions, and Executive Functioning: Revisiting Principles of Brain Organization

Abstract

In the 1800s, Dr. Paul Broca observed that patients with expressive aphasia, which is sometimes termed motor aphasia, had lesions in the anterior frontal lobe. Dr. Wernicke later reported that certain patients had an aphasia characterized by a primary comprehension deficit. These patients had lesions within the posterior lobes of the brain. However, both patient groups had one issue in common: in right-handed patients, the lesions were localized to the left hemisphere. Many years later, certainly in the 1960s and 1970s, when the study of memory was in its infancy, it was observed that patients with left hemisphere lesions had more trouble in learning new verbal material, and patients with right hemisphere lesions had greater difficulty in acquiring and remembering “non-verbal” material, such as learning and remembering newly presented designs. These and other related findings led to the idea that the left hemisphere was a language processor and that the right hemisphere was a processor of “non-verbal” and primarily spatial information. The performances on various clinical testing tasks were inexorably assigned to one or the other hemisphere. In this way, information processing became “fixed” and neuropsychological tests became “easy” to interpret. Neuropsychology and related disciplines adopted these ideas as a primary principle of brain organization. This is known as the verbal–non-verbal dichotomy of functioning between the left and right hemispheres. It has also been referred to as the language-visuospatial dichotomy of hemispheric organization. These inferences and conclusions made about brain-behavior organization were based upon a “lesion model.” The lesion model demonstrated how a person functioned without that brain region that was damaged. This model was appropriate for the technologies that were available during that era.