S. Carlson, S. Martinkauppi, P. Rama, E. Salli, A. Korvenoja, and H.J. Aronen.
  <b>Distribution of cortical activation during visuospatial
  n-back tasks as revealed by functional magnetic resonance imaging</b>.
  <i>Cereb Cortex</i>, 8(8):743-752, 1998.<br />