Determining the Relationship between White Matter Volume and Processing Speed in Adolescence

Abstract

Neuroimaging techniques have recently been used to research and identify relationships between structure and function. Because adolescence is a critical period for development of the brain, the present study's goal was to identify the possible relationships between white matter (WM) volume and processing speed during this period. White matter was of particular interest as it consists of the myelinated axons of some nerve cells which are essential for nervous system functioning. The WM volume of 157 adolescents (ages 12-17) were determined from T1-weighted images via FMRIB's Automated Segmentation Tool (FAST), whereby the brain was separated into WM, gray matter (GM), and cerebral spinal fluid (CSF). A composite score for processing speed was indicated by a z-normalized mean score from the Wechsler Abbreviated Scale of Intelligence (WASI) block design test, Paced Auditory Serial Addition Test (PASAT), Delis-Kaplan Executive Function System (D-KEFS) which included raw scores of Color-Word Conditions 1-4, verbal and spatial working memory 2-back tasks, and the hit reaction time score from the Continuous Performance Test (CPT). Results suggested that there was a small positive relationship between WM volume and age at the time of the scan, which agrees with several reported literatures. Processing speed was defined as a more negative value below the mean; the initial hypothesis was further supported as a negative relationship between WM volume and age to processing speed in adolescence observed. Although the correlation and significance was relatively low between the variables, the sample suggests that as an adolescent's WM volume or age increased or decreased, processing speed was reflected as marginally quicker or slower. INTRODUCTION AND BACKGROUNDThe human brain is primarily composed of grey matter (GM) and white matter (WM). GM consists of neuronal cell bodies, neuropil, glial cells, synapses, and capillaries, while WM is primarily composed of glial cells and myelinated axons. The GM's color represents the neuronal cell bodies, while WM's color is due to the myelin sheath. As an insulator on certain axons, myelin increases the speed of signal impulses via saltatory conduction. WM functions to connect areas of GM and sends these signals to a variety of regions including the brainstem and limbic system [1]. These signals are used as the nervous system's communication, and can be translated into cognitive functioning processes or motor processes [1,7]. The speed of the signal transmitted is related to the thickness and degree of myelination, and damage to aforementioned regions results in a reduction in functional processing speed [30]. Diseases that damage WM or myelin, such as Alzheimer's, multiple sclerosis (MS), or other factors like lesions also result in reduced function or ability to send these signals [6,10,32].In the developmental period of adolescence, both GM and WM undergo varying structural maturation [16,18,23,31]. However, increases in GM volumes peak well before an individual's 20's, wherea...