Biomedical Engineering Reference
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tor its needs over time (as opposed to doing so in a stimulus response fashion),
and to select environmental opportunities that fulfill these needs. A number of
motivational states can be present concurrently (e.g., while running across a
parking lot to catch a train you become hot, tired, and short-of-breath). Homeo-
static and biological control of thermoregulation, oxygen saturation of hemoglo-
bin, osmolality, or glucose level can be balanced against inter-organism and
social objectives related to defense, shelter, procreation, hierarchical ordering,
and curiosity. The collective neuronal and physiological processes that mediate
drives based on such needs, and linked intentional activity that meets these
needs via behavioral processes inclusive of decision-making, speech, and imagi-
nation, can be collectively referred to as motivation.
Current models of motivational function developed as a challenge to the
model of behaviorism. The behaviorist model postulated that goal-objects in the
environment have organizing effects on behavior through "stimulus-response"
relationships. In this construct, "rewards" were goal-objects or stimuli that pro-
duced repeated approach behaviors or response repetitions. A rewarding stimu-
lus could act via a memory or via salient sensory properties (i.e., a food odor) to
be an
incentive
for approach behavior. In contrast, a rewarding stimulus that
increased the probability that preceding behavioral responses would be repeated
(i.e., drug self-administration) would
reinforce
previous behavior. This behav-
ioral perspective had difficulties with concepts such as target detection by the
brain (41). Likewise, its stimulus-response framework did not allow for sym-
bolic manipulation as described by Chomskian linguistics (95), or inferential
processes (178). These deficiencies instigated conceptual revolts in the form of
cognitive neuroscience (113,139,165,176), neuro-computation (123,58,169,56),
judgment and decision making (172,238), emotion neuroscience (69,146,196),
behavioral ecology and neuroeconomics (102,140), and a more "pragmatist"
perspective framed by nonlinear dynamics (95,96), and the effects of nonlinear
processes on system information (109,110,267).
Synthesizing these viewpoints, a general schema for motivation functions is
illustrated in Figure 2a. This schema for a Motivation Information Theoretic
(MIT) model is generally consistent with recent neuro-computational evidence
(75,96,243). In the MIT model, at least three fundamental operations can be
ascribed to motivated behavior (33), which have precursors in models of animal
cognitive physiology function and communication theory (234) (Figure 2b,c).
These operations include a number of processes. One grouping of processes (A)
includes evaluation of homeostatic and social needs, and selection of objectives
to meet these needs. A second grouping of processes (B) includes sensory per-
ception of potential goal-objects that may meet these objectives, assessment of
potential reward/aversion outcomes related to these goal-objects, and compari-
son of these assessments against memory of prior outcomes. A third grouping
(C) involves assessment, planning, and execution of action to obtain or avoid
these outcomes (33,119,120,167,168,206,237,238). As these operations rely on
