The effects of age on the neurocognitive architecture of verbal and spatial working memory.

This study addressed the effects of age and memory load on the neural substrates of verbal and spatial working memory. Using fMRI, 21 young adults and 23 seniors were scanned while performing verbal and spatial delayed-response tasks in which memory load was manipulated. The event-related design allowed for the separation of encoding-, maintenance-, and retrieval-related neural activity. While many neuroimaging studies have examined the effects of memory load, stimulus type, and age on the neural correlates of working memory individually, this experiment is unique in that no study has combined them in a single set of subjects. In young adults, analyses revealed regional load-sensitivity during verbal and spatial working memory. Regional load-sensitivity was observed during verbal maintenance and spatial retrieval, suggesting that the load manipulation affected verbal and spatial working memory at different stages of processing. Analyses also revealed that young adults and seniors activated strikingly similar neural networks during verbal and spatial working memory, suggesting the neurocognitive architecture of working memory remains stable across the lifespan. However, several important age-differences emerged during the maintenance interval. First, while verbal maintenance-related neural activity was largely left-lateralized in the two groups at the two lower memory loads, young adults also activated the right hemisphere extensively at the high verbal memory load, whereas seniors did not. This finding may represent the neural correlate of age-related declines in working memory capacity. Second, during verbal and spatial working memory, at a low memory load, while performance accuracy was age-equivalent, seniors activated right DLPFC more than young adults. However, at the high memory load, seniors were less accurate than young adults and also activated right DLPFC to a lesser degree than young adults. This suggests that at low levels of memory load, seniors can maintain performance in the face of age-related declines in the neural circuitry of working memory via the recruitment of DLPFC-mediated mechanisms. However, at high levels of memory load, these results suggest that have seniors have reached a capacity limitation at which DLPFC recruitment is not sufficient to maintain performance.Ph.D.Biological SciencesCognitive psychologyNeurosciencesPsychobiologyPsychologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126108/2/3237918.pd

Neural Changes following Remediation in Adult Developmental Dyslexia

AbstractBrain imaging studies have explored the neural mechanisms of recovery in adults following acquired disorders and, more recently, childhood developmental disorders. However, the neural systems underlying adult rehabilitation of neurobiologically based learning disabilities remain unexplored, despite their high incidence. Here we characterize the differences in brain activity during a phonological manipulation task before and after a behavioral intervention in adults with developmental dyslexia. Phonologically targeted training resulted in performance improvements in tutored compared to nontutored dyslexics, and these gains were associated with signal increases in bilateral parietal and right perisylvian cortices. Our findings demonstrate that behavioral changes in tutored dyslexic adults are associated with (1) increased activity in those left-hemisphere regions engaged by normal readers and (2) compensatory activity in the right perisylvian cortex. Hence, behavioral plasticity in adult developmental dyslexia involves two distinct neural mechanisms, each of which has previously been observed either for remediation of developmental or acquired reading disorders