Implementing Neuroscience Principles to Support Habilitation and ...

CNS's ability to decrease its responsiveness to specific stimuli
at any given moment. Although neuroscientists frequently
discuss descending inhibition (i.e., higher centers having
an effect on lower centers), the CNS is rich with interneuron
networks that can inhibit neighboring cells (i.e., lateral inhibition).
Lateral inhibition helps make target stimuli stronger
and clearer, which contributes to organization and integration
of information for the CNS.
Feedback and Feedforward Mechanisms
Feedback is the CNS's ability to send information back
to itself as a check and balance. This enables the person to
judge whether actions already initiated need to be modified
for the future. Nohack & Dernerest ( 198 I ) describe two general
types of feedback: local feedback and reflected feedback.
Local feedback inhibition occurs when small interncurons
within a neighboring circuit form connections that stop
a stimulus that has been occurring in a large neuron. This
mechanism helps keep activity froin continuing beyond its
iiseful period. For example, a local feedback circuit can stop
the ongoing firing of a niotor neuron by sending an inhibitory
signal to the motor nerve, thus allowing a pcrson to relax
the muscle and stop the movement. This inhibition, however,
occurs only if the local circuit neuron information is stronger
than other messages on that large motor neuron. Reflected
feedback occurs when higher CNS centers send descending
fibers to influence the sensory or niotor neurons. These higher
centers can send excitatory or inhibitory messages making
it either easier or more difiicult to activate the neurons.
Feedforward circuits exert influence in a forward direction
coinciding with the information flow of the neurons.
This most frequently occurs in ascending sensory system
pathways to either alert higher centers about incoming information
or inhibit some areas in order to strengthen the focus
of more important parts of the environmental stimuli. Feedforward
inhibition is critical for task performance, because
people always are confronted with more stimuli than are
needed to complete the task successfully.
Intersensory Integration
Intersensory integration is a critical feature of the CNS.
Interneurons in the spinal cord participate in primitive intersensory
integration, however the brain stem is a primary site
for this activity. Nuclei in the brain stem receive input from
several sensory sources, allowing organization and integration
of information at this level. For example, the vestibular
nuclei receive input from the vestibular organ, the visual system
and the proprioceptors. This intersensory integration
supports the development of a multidimensional map of self
and environment and a map of how self and environment
interact appropriately.
Plasticity
Plasticity is the CNS's ability to adapt structurally or
functionally in response to environmental demands.
Previously, neuroscientists believed that plasticity was most
evident during the prenatal stage and childhood; now
researchers have found that there are various types of internal
and external environmental alterations that support or
inhibit the manifestations of plasticity (Lund, 1978). When
individuals participate in interventions that require more
functional patterns of movement, they receive organized patterns
of sensory feedback that may alter the internal environment,
creating opportunities for axon reorganization, altered
synaptic activity, or dendritic branching, just as enriched
environments support these actions during the developmental
periods (Bach-y-Rita, 1980; Moore, 1980). Such findings
challenge innovative rehabilitation practice.
Compensatory Action of the CNS
Parts of the CNS are interdependent (Moore, 1980).
When damage occurs to one or more portions of the system,
the interdependency relationships are disrupted; the resulting
observable behaviors and performance are hypothesized to
be compensating for the loss of information from one of its
members. This compensatory model suggests that the CNS
centers do not function on their own to initiate action, but
work as part of a network in the CNS to enable a particular
action. When data are not available to the system because of
damage, the network is disrupted, making it difficult for a
particular action to occur. Destructive behavior is the result
of an incomplete and compensating CNS.
Summary
The principles of centrifugal control, balance of excitation
and inhibition, plasticity, and compensatory action are
basic and must be used to design interventions that support
occupational performance. Interventions that conflict with
these basic principles compromise the person by not
enabling them to profit from the therapeutic experience.
The olfactory (smell) and gustatory (taste) systems are
primitive, chemically-based sensory systems signaling the
CNS about odors and tastes. The somatosensory, proprioceptive
and vestibular systems enable an individual to develop
an accurate map of self and how one interacts with the environment.
Finally, the visual and auditory systems are responsible
for mapping environmental variables so that interaction
with the environment can he accurate and reliable.