The influence of working-memory demand and subject performance on prefrontal cortical activity. Rypma, B., Berger, J. S., & D'Esposito, M. J Cogn Neurosci, 14(5):721–731, 2002.
doi  abstract   bibtex   
Brain imaging and behavioral studies of working memory (WM) converge to suggest that the ventrolateral prefrontal cortex (PFC) mediates a capacity-limited storage buffer and that the dorsolateral PFC mediates memory organization processes that support supracapacity memory storage. Previous research from our laboratory has shown that the extent to which such memory organization processes are required depends on both task factors (i.e., memory load) and subject factors (i.e., response speed). Task factors exert their effects mainly during WM encoding while subject factors exert their effects mainly during WM retrieval. In this study, we sought to test the generalizability of these phenomena under more difficult memory-demand conditions than have been used previously. During scanning, subjects performed a WM task in which they were required to maintain between 1 and 8 letters over a brief delay. Neural activity was measured during encoding, maintenance, and retrieval task periods using event-related functional magnetic resonance imaging. With increasing memory load, there were reaction time increases and accuracy rate decreases, ventrolateral PFC activation decreases during encoding, and dorsolateral PFC activation increases during maintenance and retrieval. These results suggest that the ventrolateral PFC mediates WM storage and that the dorsolateral PFC mediates strategic memory organization processes that facilitate supracapacity WM storage. Additionally, high-performing subjects showed overall less activation than low-performing subjects, but activation increases with increasing memory load in the lateral PFC during maintenance and retrieval. Low-performing subjects showed overall more activation than high-performing subjects, but minimal activation increases in the dorsolateral PFC with increasing memory load. These results suggest that individual differences in both neural efficiency and cognitive strategy underlie individual differences in the quality of subjects' WM performance.
@Article{Rypma2002,
  author      = {Rypma, Bart and Berger, Jeffrey S. and D'Esposito, Mark},
  journal     = {J Cogn Neurosci},
  title       = {The influence of working-memory demand and subject performance on prefrontal cortical activity.},
  year        = {2002},
  number      = {5},
  pages       = {721--731},
  volume      = {14},
  abstract    = {Brain imaging and behavioral studies of working memory (WM) converge
	to suggest that the ventrolateral prefrontal cortex (PFC) mediates
	a capacity-limited storage buffer and that the dorsolateral PFC mediates
	memory organization processes that support supracapacity memory storage.
	Previous research from our laboratory has shown that the extent to
	which such memory organization processes are required depends on
	both task factors (i.e., memory load) and subject factors (i.e.,
	response speed). Task factors exert their effects mainly during WM
	encoding while subject factors exert their effects mainly during
	WM retrieval. In this study, we sought to test the generalizability
	of these phenomena under more difficult memory-demand conditions
	than have been used previously. During scanning, subjects performed
	a WM task in which they were required to maintain between 1 and 8
	letters over a brief delay. Neural activity was measured during encoding,
	maintenance, and retrieval task periods using event-related functional
	magnetic resonance imaging. With increasing memory load, there were
	reaction time increases and accuracy rate decreases, ventrolateral
	PFC activation decreases during encoding, and dorsolateral PFC activation
	increases during maintenance and retrieval. These results suggest
	that the ventrolateral PFC mediates WM storage and that the dorsolateral
	PFC mediates strategic memory organization processes that facilitate
	supracapacity WM storage. Additionally, high-performing subjects
	showed overall less activation than low-performing subjects, but
	activation increases with increasing memory load in the lateral PFC
	during maintenance and retrieval. Low-performing subjects showed
	overall more activation than high-performing subjects, but minimal
	activation increases in the dorsolateral PFC with increasing memory
	load. These results suggest that individual differences in both neural
	efficiency and cognitive strategy underlie individual differences
	in the quality of subjects' WM performance.},
  doi         = {10.1162/08989290260138627},
  institution = {Department of Psychology, Rutgers University, Smith Hall, 101 Warren Street, Newark, NJ 07102, USA. rypma@psychology.rutgers.edu},
  keywords    = {Adult; Cognition, physiology; Female; Humans; Magnetic Resonance Imaging; Male; Memory, Short-Term, physiology; Prefrontal Cortex, physiology},
  language    = {eng},
  medline-pst = {ppublish},
  pmid        = {12167257},
  timestamp   = {2014.04.27},
}

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