schemes) seem to be located in (or at least controlled by) the lateral prefrontal
areas of the brain (Brodmann Areas—BA 9, 46, 45, 44, 47; e.g., Goldman-
Rakic, 1995; Muller, Machado, & Knight, 2002). However “the precise func-
tioning and neural implementation of these executive functions is still unre-
solved” (Szameitat, Schubert, Muller, & von Cramon, 2002, p. 1184).
MA2. The second constituent is a mental energy or scheme-booster ca-
pacity, which we call theM-operator—a limited resource that grows in power
(i.e., in the number of schemes that it can boost simultaneously) throughout
childhood until adolescence. The hyperactivation of schemes by this resource
helps to produce what James (1892/1961) and others (e.g., Crick, 1994) have
called the beam of mental attention. Figure 8.1 denotes byHthe schemes
upon whichM-capacity is applied at the moment; and it denotes byH′other
schemes in the subject’s repertoire that currently are not attended to.M-ca-
pacity increases endogenously from the first month of age up to adolescence,
according to an idealized schedule that, when measured behaviorally in terms
of the number of schemes that it can boost simultaneously, appears in Tables
8.1 and 8.2. In these tables, the total measure ofM-capacity (i.e.,M-power) is
divided in two parts: the “e” and the “k” components. The “e” component is
theM-capacity that emerges during the sensorimotor period, and which at
the end of this period is equal to 6 (sensorimotor schemes beingM-boosted si-
multaneously). The “k” component is theM-capacity that emerges from 3
years of age onward, reaching the asymptotic value of 7 mental schemes at
15–16 years. Notice that we are estimating behaviorally the amount of
attentional capacity available at a certain age, in terms of the number of
schemes that can be simultaneouslyM-boosted. Because the sensorimotor
schemes and their network connections are much simpler (and so would need
less mental energy) than the schemes from subsequent mental stages, the “e”
scale (described in Table 8.1) and the “k” scale (Table 8.2) should not be com-
bined or confounded. Although this model for estimating mental attentional
capacity is still controversial, there is much experimental-developmental re-
search that supports it (see Case, 1998; Pascual-Leone, 1987, 1989, 1995,
1997, 2000a; Pascual-Leone & Johnson, 2001). To appreciate and use the
present chapter, however, the reader need not accept our quantification of
mental attention. It will suffice to accept that mental attention grows with age
and that task analytical methods can be used to rank tasks in terms of their
relative mental-attentional demand.
We think that the anterior cingulate gyrus, a limbic structure that Allman
et al. (2001) considered to be part of the neocortex, and several subcortical
brain structures (e.g., basal ganglia, cortical and subcortical connections with
reticular formation, and thalamic reticular complex) are part of the still un-
clear brain organization that constitutesM-capacity. Prefrontal areas related
toM-capacity control are those of the lateral prefrontal cortex: ventrolateral
206 PASCUAL-LEONE AND JOHNSON