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Cortical modulation of auditory processing in the midbrain.

Bajo VM, King AJ - Front Neural Circuits (2013)

Bottom Line: Focal electrical stimulation and inactivation studies have shown that the auditory cortex can modify almost every aspect of the response properties of IC neurons, including their sensitivity to sound frequency, intensity, and location.Along with other descending pathways in the auditory system, the corticocollicular projection appears to continually modulate the processing of acoustical signals at subcortical levels.In particular, there is growing evidence that these circuits play a critical role in the plasticity of neural processing that underlies the effects of learning and experience on auditory perception by enabling changes in cortical response properties to spread to subcortical nuclei.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Anatomy and Genetics, University of Oxford Oxford, UK.

ABSTRACT
In addition to their ascending pathways that originate at the receptor cells, all sensory systems are characterized by extensive descending projections. Although the size of these connections often outweighs those that carry information in the ascending auditory pathway, we still have a relatively poor understanding of the role they play in sensory processing. In the auditory system one of the main corticofugal projections links layer V pyramidal neurons with the inferior colliculus (IC) in the midbrain. All auditory cortical fields contribute to this projection, with the primary areas providing the largest outputs to the IC. In addition to medium and large pyramidal cells in layer V, a variety of cell types in layer VI make a small contribution to the ipsilateral corticocollicular projection. Cortical neurons innervate the three IC subdivisions bilaterally, although the contralateral projection is relatively small. The dorsal and lateral cortices of the IC are the principal targets of corticocollicular axons, but input to the central nucleus has also been described in some studies and is distinctive in its laminar topographic organization. Focal electrical stimulation and inactivation studies have shown that the auditory cortex can modify almost every aspect of the response properties of IC neurons, including their sensitivity to sound frequency, intensity, and location. Along with other descending pathways in the auditory system, the corticocollicular projection appears to continually modulate the processing of acoustical signals at subcortical levels. In particular, there is growing evidence that these circuits play a critical role in the plasticity of neural processing that underlies the effects of learning and experience on auditory perception by enabling changes in cortical response properties to spread to subcortical nuclei.

No MeSH data available.


Inputs from different auditory centers converge in the IC. (A) A small fluorogold tracer injection in the ventromedial part of the IC central nucleus of the gerbil produces retrograde labeling of neurons in the MSO, periolivary nuclei, VNLL, and A1 on the same side, in the cochlear nuclei and IC on the opposite side, and in the LSO, DCN, and DNLL on both sides. (B) Retrogradely labeled cells in the cortex are found mainly in layer V after a rhodamine tracer injection in the IC. (C) Large labeled pyramidal cell with the soma located in cortical layer V and (D) a tufted dendritic tree ending in layer I. Calibration bars: 1 mm (A), 0.2 mm (B), and 25 μm (C,D). Modified with permission from Bajo and Moore (2005).
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Figure 1: Inputs from different auditory centers converge in the IC. (A) A small fluorogold tracer injection in the ventromedial part of the IC central nucleus of the gerbil produces retrograde labeling of neurons in the MSO, periolivary nuclei, VNLL, and A1 on the same side, in the cochlear nuclei and IC on the opposite side, and in the LSO, DCN, and DNLL on both sides. (B) Retrogradely labeled cells in the cortex are found mainly in layer V after a rhodamine tracer injection in the IC. (C) Large labeled pyramidal cell with the soma located in cortical layer V and (D) a tufted dendritic tree ending in layer I. Calibration bars: 1 mm (A), 0.2 mm (B), and 25 μm (C,D). Modified with permission from Bajo and Moore (2005).

Mentions: The traditional view of the central auditory pathway begins with the auditory nerve fibers entering and bifurcating in the cochlear nuclei from where information is transmitted successively via other centers in the brainstem, midbrain, and thalamus to the auditory cortex, where further processing gives rise to our perception of the auditory world. According to this hierarchical view of the ascending pathways, the inferior colliculus (IC) in the midbrain is usually regarded as an obligatory relay for the transmission of auditory signals (e.g., Aitkin and Phillips, 1984). When a retrograde tracer injection is placed in the IC, however, more cells are labeled in the auditory cortex than in brainstem centers such as the cochlear nuclei or superior olivary complex (Figure 1A). Consequently, processing in the IC must be influenced by cortical outputs. In fact, descending projections connect almost all levels of the auditory pathway, indicating that a bidirectional flow of information takes place.


Cortical modulation of auditory processing in the midbrain.

Bajo VM, King AJ - Front Neural Circuits (2013)

Inputs from different auditory centers converge in the IC. (A) A small fluorogold tracer injection in the ventromedial part of the IC central nucleus of the gerbil produces retrograde labeling of neurons in the MSO, periolivary nuclei, VNLL, and A1 on the same side, in the cochlear nuclei and IC on the opposite side, and in the LSO, DCN, and DNLL on both sides. (B) Retrogradely labeled cells in the cortex are found mainly in layer V after a rhodamine tracer injection in the IC. (C) Large labeled pyramidal cell with the soma located in cortical layer V and (D) a tufted dendritic tree ending in layer I. Calibration bars: 1 mm (A), 0.2 mm (B), and 25 μm (C,D). Modified with permission from Bajo and Moore (2005).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3539853&req=5

Figure 1: Inputs from different auditory centers converge in the IC. (A) A small fluorogold tracer injection in the ventromedial part of the IC central nucleus of the gerbil produces retrograde labeling of neurons in the MSO, periolivary nuclei, VNLL, and A1 on the same side, in the cochlear nuclei and IC on the opposite side, and in the LSO, DCN, and DNLL on both sides. (B) Retrogradely labeled cells in the cortex are found mainly in layer V after a rhodamine tracer injection in the IC. (C) Large labeled pyramidal cell with the soma located in cortical layer V and (D) a tufted dendritic tree ending in layer I. Calibration bars: 1 mm (A), 0.2 mm (B), and 25 μm (C,D). Modified with permission from Bajo and Moore (2005).
Mentions: The traditional view of the central auditory pathway begins with the auditory nerve fibers entering and bifurcating in the cochlear nuclei from where information is transmitted successively via other centers in the brainstem, midbrain, and thalamus to the auditory cortex, where further processing gives rise to our perception of the auditory world. According to this hierarchical view of the ascending pathways, the inferior colliculus (IC) in the midbrain is usually regarded as an obligatory relay for the transmission of auditory signals (e.g., Aitkin and Phillips, 1984). When a retrograde tracer injection is placed in the IC, however, more cells are labeled in the auditory cortex than in brainstem centers such as the cochlear nuclei or superior olivary complex (Figure 1A). Consequently, processing in the IC must be influenced by cortical outputs. In fact, descending projections connect almost all levels of the auditory pathway, indicating that a bidirectional flow of information takes place.

Bottom Line: Focal electrical stimulation and inactivation studies have shown that the auditory cortex can modify almost every aspect of the response properties of IC neurons, including their sensitivity to sound frequency, intensity, and location.Along with other descending pathways in the auditory system, the corticocollicular projection appears to continually modulate the processing of acoustical signals at subcortical levels.In particular, there is growing evidence that these circuits play a critical role in the plasticity of neural processing that underlies the effects of learning and experience on auditory perception by enabling changes in cortical response properties to spread to subcortical nuclei.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Anatomy and Genetics, University of Oxford Oxford, UK.

ABSTRACT
In addition to their ascending pathways that originate at the receptor cells, all sensory systems are characterized by extensive descending projections. Although the size of these connections often outweighs those that carry information in the ascending auditory pathway, we still have a relatively poor understanding of the role they play in sensory processing. In the auditory system one of the main corticofugal projections links layer V pyramidal neurons with the inferior colliculus (IC) in the midbrain. All auditory cortical fields contribute to this projection, with the primary areas providing the largest outputs to the IC. In addition to medium and large pyramidal cells in layer V, a variety of cell types in layer VI make a small contribution to the ipsilateral corticocollicular projection. Cortical neurons innervate the three IC subdivisions bilaterally, although the contralateral projection is relatively small. The dorsal and lateral cortices of the IC are the principal targets of corticocollicular axons, but input to the central nucleus has also been described in some studies and is distinctive in its laminar topographic organization. Focal electrical stimulation and inactivation studies have shown that the auditory cortex can modify almost every aspect of the response properties of IC neurons, including their sensitivity to sound frequency, intensity, and location. Along with other descending pathways in the auditory system, the corticocollicular projection appears to continually modulate the processing of acoustical signals at subcortical levels. In particular, there is growing evidence that these circuits play a critical role in the plasticity of neural processing that underlies the effects of learning and experience on auditory perception by enabling changes in cortical response properties to spread to subcortical nuclei.

No MeSH data available.