Promoting Growth in Behavioral Neurology: A Path Forward.

Behavioral neurology & neuropsychiatry (BNNP) is a field that seeks to understand brain-behavior relationships, including fundamental brain organization principles and the many ways that brain structures and connectivity can be disrupted, leading to abnormalities of behavior, cognition, emotion, perception, and social cognition. In North America, BNNP has existed as an integrated subspecialty through the United Council for Neurologic Subspecialties since 2006. Nonetheless, the number of behavioral neurologists across academic medical centers and community settings is not keeping pace with increasing clinical and research demand. In this commentary, we provide a brief history of BNNP followed by an outline of the current challenges and opportunities for BNNP from the behavioral neurologist's perspective across clinical, research, and educational spheres. We provide a practical guide for promoting BNNP and addressing the shortage of behavioral neurologists to facilitate the continued growth and development of the subspecialty. We also urge a greater commitment to recruit trainees from diverse backgrounds so as to dismantle persistent obstacles that hinder inclusivity in BNNP-efforts that will further enhance the growth and impact of the subspecialty. With rapidly expanding diagnostic and therapeutic approaches across a range of conditions at the intersection of neurology and psychiatry, BNNP is well positioned to attract new trainees and expand its reach across clinical, research, and educational activities.

One of the most well-established age-related changes in neural activity disappears after controlling for visual acuity.

Numerous studies using a variety of imaging techniques have reported age-related differences in neural activity while subjects carry out cognitive tasks. Surprisingly little attention has been paid to the potential impact of age-associated changes in sensory acuity on these findings. Studies in the visual modality frequently report that their subjects had "normal or corrected- to-normal vision." However, in most cases, there is no indication that visual acuity was actually measured, and it is likely that the investigators relied largely on self-reported visual status of subjects, which is often inaccurate. We investigated whether differences in visual acuity influence one of the most commonly observed findings in the event-related potentials literature on cognitive aging, a reduction in posterior P3b amplitude, which is an index of cognitive decision-making/updating. Well-matched young (n=26) and old adults (n=29) participated in a visual oddball task. Measured visual acuity with corrective lenses was worse in old than young adults. Results demonstrated that the robust age-related decline in P3b amplitude to visual targets disappeared after controlling for visual acuity, but was unaffected by accounting for auditory acuity. Path analysis confirmed that the relationship between age and diminished P3b to visual targets was mediated by visual acuity, suggesting that conveyance of suboptimal sensory data due to peripheral, rather than central, deficits may undermine subsequent neural processing. We conclude that until the relationship between age-associated differences in visual acuity and neural activity during experimental tasks is clearly established, investigators should exercise caution attributing results to differences in cognitive processing.

Investigating age-related changes in anterior and posterior neural activity throughout the information processing stream.

Event-related potential (ERP) and other functional imaging studies often demonstrate age-related increases in anterior neural activity and decreases in posterior activity while subjects carry out task demands. It remains unclear whether this "anterior shift" is limited to late cognitive operations like those indexed by the P3 component, or is evident during other stages of information processing. The temporal resolution of ERPs provided an opportunity to address this issue. Temporospatial principal component analysis (PCA) was used to identify underlying components that may be obscured by overlapping ERP waveforms. ERPs were measured during a visual oddball task in 26 young, 26 middle-aged, and 29 old subjects who were well-matched for IQ, executive function, education, and task performance. PCA identified six anterior factors peaking between ∼140 ms and 810 ms, and four posterior factors peaking between ∼300 ms and 810 ms. There was an age-related increase in the amplitude of anterior factors between ∼200 and 500 ms, and an age-associated decrease in amplitude of posterior factors after ∼500 ms. The increase in anterior processing began as early as middle-age, was sustained throughout old age, and appeared to be linear in nature. These results suggest that age-associated increases in anterior activity occur after early sensory processing has taken place, and are most prominent during a period in which attention is being marshaled to evaluate a stimulus. In contrast, age-related decreases in posterior activity manifest during operations involved in stimulus categorization, post-decision monitoring, and preparation for an upcoming event.