Adolescence is the stage of development that begins at about age 11 or 12 years and continues through the teen years until it ends, at least in Western cultures, in the early to mid-20s with the attainment of social, emotional, and financial independence. We think of adolescence as a time of significant physical and psychosocial changes, as teens gain inches and pounds; go through puberty; separate emotionally from parents to affiliate with peers; develop relationships and a sense of identity; and ultimately make the transition to independent young adulthood. Adolescence also is a time of significant brain and cognitive development and, related to these developments, significant changes in communication functions. In this article, we summarize key brain and cognitive development during adolescence, with a focus on the development of executive functions (EFs) and how these functions are evaluated, and illustrate links between EFs and communication disorders in two clinical populations.
Adolescent Brain and Cognitive Development
Adolescence is characterized by both an increase in white-matter volume (myelination), which is a continuation of changes throughout childhood, and changes in grey-matter volume. Grey-matter changes are complex, beginning with an increase in grey-matter volume in preadolescence, which is thought to reflect a wave of synaptogenesis (production of new synapses), followed by a decrease as those new synapses are pruned back. In other words, adolescent brain development seems to echo what is seen during the first two years of life, when the brain is particularly sensitive to factors such as hormones and environmental input. These grey- and white-matter changes are not uniform throughout the brain, as certain regions seem to be more plastic during this stage.
The region that has received the most attention in the adolescent research literature is the prefrontal cortex (PFC). There continues to be debate about the exact nature of PFC developments in adolescence, but researchers agree on three main points:
- The PFC and its connections undergo significant changes during adolescence.
- These changes underlie important cognitive developments.
- The timeline for PFC development is variable across adolescents and even adults; some people never attain what might be called "mature" frontal lobes.
White matter and PFC changes during adolescence are thought to underlie two main cognitive developments critical to communication: increased speed of processing and improvements in EFs. "Speed of processing" describes the time required to perform mental operations and generate a response, such as making rapid inferences and following topic shifts in a conversation, decoding overlapping input from multiple speakers, and formulating quick responses to questions. Speed of processing is measured using timed tests such as rapid naming [e.g., the Rapid Automatized Naming Test (Wolf & Denkla, 2005)]; comprehension of rapidly presented auditory information [e.g., the Speed and Capacity of Language Processes Test (Baddeley, Elmslie, & Nimmo Smith, 1992)]; or calculation-based tests [e.g., the Paced Auditory Serial Addition Task (Gronwall & Sampson, 1974)].
"Executive functions" are complex cognitive control mechanisms that allow for goal-oriented behavior, and include updating working memory, cognitive flexibility, inhibition of irrelevant information, and self-control (Miyake et al., 2000). There is growing evidence that EFs continue to develop through late adolescence and into adulthood (for review, see Crone, 2009), and are related to important outcomes such as academic achievement (Latzman, Elkovitch, Young, & Clark, 2010). Together with increases in information-processing speed, EF improvements facilitate development of more abstract and efficient processing of language, which is reflected in adolescent language developments such as use of complex syntax (e.g., multiple embedded clauses), abstract language use, and skills such as debate and persuasion (Nippold, 1998).
These skills are evident in both spoken and written language, and allow students to meet increasingly complex academic demands. As Singer and Bashir (1999) state, students learn to "make plans, discuss, evaluate ideas, participate in groups, reflect on their work, change their minds, and rewrite their papers" (p. 267). The complexity of these communication tasks and the expectation that they will be completed independently increase substantially in adolescence. EFs also are critical in social conversations, which require the ability to maintain and update information as the conversation progresses, inhibit distracting stimuli to stay on topic, and formulate relevant ideas to respond appropriately to conversational partners.
Assessment of EFs
As EFs include several cognitive processes, assessment may either focus on specific sub-skills (e.g., working memory or inhibition) or evaluate activities in everyday life. The Delis-Kaplan Executive Function Systems (D-KEFS; Delis, Kaplan, & Karmer, 2001), which is used by neuropsychologists to assess EFs, is an example of a sub-skill assessment, and includes tests of specific skills such as inhibition and mental flexibility. The Wisconsin Card Sorting Task (WCST; Heaton, 1981), another example of a relatively specific test, requires examinees to sort cards based on dimensions such as shape or color. Sorting rules change throughout the task, requiring examinees to adjust their sorting rules flexibly while inhibiting previous sorting strategies.
Standardized tests of EF sub-skills have been widely criticized for their lack of ecological validity, in part because they typically bear little resemblance to the way EFs are used in everyday life. Also, given that EFs are used primarily for independent goal-oriented behavior (i.e., self-structured behavior in novel situations), these highly structured tests can mask deficits that would be evident outside of the clinic. Thus, adolescents who can organize their thoughts and complete academic assignments in a treatment session may fail to do so in real school settings.
Reprinted with permission from "Executive Functions and Communication in Adolescents" by Lyn S. Turkstra and Lindsey J. Byom. The ASHA Leader, 15, December 21, 2010, pp. 8-11. Copyright 2010. All rights reserved.