FEEDFORWARD & FEEDBACK PATTERNS
 
 
  1. A)The functional organization of the auditory system includes feedforward connections (from the inner ear through the brainstem nuclei, midbrain nuclei, thalamus up to the auditory cortex; functionally, this type of „forward“ processing is called „bottom-up“) and feedback connections (in the reverse direction; functionally, this is called „top-down“ processing). The function of the feedback connections is under investigation, but it appears as if subcortically they regulate the „gain“ of the central auditory system and play a role in regulating subcortical and cortical plasticity.

  2. B)The auditory cortex is organized into a multitude of areas with different functions. Traditionally, the fields that receive the main input from the so-called lemniscal auditory system and that show shortest response latencies are considered „primary“ (in the cat, these are the fields A1 and AAF). With corticocortical connections these fields relay the incoming information into the higher-order areas (DZ, PAF, ED, A2, etc.). The cortex is structured into 6 layers. Layer III is the source of the feedforward cortical connections, the layers I, V and VI receive feedback connections. 

  3. The function of the individual auditory areas is still under investigation, but most likely the primary areas represent features of the auditory object that the cortex is processing (e.g. they „identify“ the frequencies the sound is composed of), the higher-order areas classify the features into these objects (they „identify“ the stimulus as e.g. a keychain fallen on the ground). Obviously, in perception, all auditory areas cooperate and constitute a functional unit that cannot easily be taken apart; nonetheless, the different function of individual areas for certain perceptual processes have been shown using lesioning (permanent or reversible lesions).  


>> continue on the function of these patterns and „Decoupling & Prediction coding“ in deafTop-down_decoupling_in_deaf.htmlshapeimage_2_link_0
 

Schematic illustration of feedforward and feedback projections in the auditory system of the cat; feedforward connections are stained blue, feedback red. Already in this simplified diagram it becomes clear that the feedback circuits are at least as abundant as the feedforward circuits. Figure from Kral and Eggermont (2007); see also an updated version of the theory in Kral et al. (2016).

Decoupling & Prediction codingTop-down_decoupling_in_deaf.htmlshapeimage_4_link_0
Additional information:
Examples of top-down effectsExamples.htmlshapeimage_6_link_0