Complex processing

CNS processing of sensory information occurs on many levels --- and in both ascending and descending directions
- basically, anytime you introduce a synapse, you create the potential for a signal to be modified
CNS connections can be either excitatory or inhibitory in nature

	Series processing refers to information that is passed in an ascending manner, from one neuron to the next within a specific pathway. in this diagram, from first order neuron to second order neuron, etc. This type of processing is a fundamental component of the labelled line theory of sensory coding.
	However, sensory information can also be expanded from the primary sensory pathway into multiple, parallel processing routes. e.g., in the auditory system, the auditory nerve branches within the cochlear nucleus to form 3 separate tonotopic maps nociceptive pathways branch to activate autonomic and emotional responses, as well as reaching somatosensory cortex
	Sensory information can also converge --- both within a pathway, and across modalities. the simplest example would be where a 2nd order neuron has a receptive field that represents the sum of the receptive fields of the 1st order neurons that synapse on it - see the discussion of simple and complex cortical cells in the visual system another example explains the gate theory of pain - stimulation of touch afferents can decrease pain perception due to convergence of inputs onto spinal cord neurons
	Lastly, there is descending control of all aspects of sensory processing. These control systems include: centrifugal connections (i.e., those that provide feedback control within a sensory system) an example of feedback control of sensory receptors occurs with modulation of outer hair cell function by efferent cells of the auditory brainstem non-sensory inputs, such as those that allow for selective attention. see the discussion of pain as an example

2007 Sensory Physiology

Complex processing