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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.


Related in: MedlinePlus

The projection from the auditory cortex to the inferior colliculus is essential for training-induced plasticity of spatial hearing in adult ferrets. (A) Lateral view of the ferret midbrain showing the location and number of injections of fluorescent microspheres conjugated with chlorine e6 in the left IC. (B) Schematic showing the selective ablation of retrogradely labeled layer V corticocollicular neurons by illumination of the ipsilateral auditory cortex with near-infrared light. (C) Sound localization accuracy (averaged across 12 speaker locations in the horizontal plane) before the right ear was plugged (Preplug), on each of the 10 days over which an ear plug was worn and following its removal (Post-plug). Data from control animals are shown in black and from the ferrets with corticocollicular lesions in red. The symbols represent different animals and the lines show the mean scores. (D) Staining with the SMI32 antibody, a marker of layer III and layer V pyramidal cortical neurons, was sparser in the left (lesioned) primary auditory cortex, resulting in a less distinct bilaminar appearance (top) than on the right side (bottom). Calibration bars: 2 mm in (A) and 0.1 mm in (D). Modified with permission from Bajo et al. (2010a).
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Figure 9: The projection from the auditory cortex to the inferior colliculus is essential for training-induced plasticity of spatial hearing in adult ferrets. (A) Lateral view of the ferret midbrain showing the location and number of injections of fluorescent microspheres conjugated with chlorine e6 in the left IC. (B) Schematic showing the selective ablation of retrogradely labeled layer V corticocollicular neurons by illumination of the ipsilateral auditory cortex with near-infrared light. (C) Sound localization accuracy (averaged across 12 speaker locations in the horizontal plane) before the right ear was plugged (Preplug), on each of the 10 days over which an ear plug was worn and following its removal (Post-plug). Data from control animals are shown in black and from the ferrets with corticocollicular lesions in red. The symbols represent different animals and the lines show the mean scores. (D) Staining with the SMI32 antibody, a marker of layer III and layer V pyramidal cortical neurons, was sparser in the left (lesioned) primary auditory cortex, resulting in a less distinct bilaminar appearance (top) than on the right side (bottom). Calibration bars: 2 mm in (A) and 0.1 mm in (D). Modified with permission from Bajo et al. (2010a).

Mentions: To address this question, Bajo et al. (2010a) used a chromophore-targeted neuronal degeneration technique to investigate the behavioral effects in ferrets of selectively eliminating layer V pyramidal cells in the primary auditory cortical areas that project to the IC (Figure 9). This involved retrogradely labeling corticocollicular projection neurons by injecting fluorescent microbeads conjugated with chlorine e6 in the IC on one side of the brain, and subsequently illuminating the ipsilateral auditory cortex with near-infrared light. This resulted in a loss of about two thirds of the A1 neurons that project to the IC, without affecting those in surrounding cortical areas. As previously discussed, most corticocollicular axons target the ipsilateral IC, so this approach allowed an assessment of the effects of removing descending axons predominantly on one side of the brain only.


Cortical modulation of auditory processing in the midbrain.

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

The projection from the auditory cortex to the inferior colliculus is essential for training-induced plasticity of spatial hearing in adult ferrets. (A) Lateral view of the ferret midbrain showing the location and number of injections of fluorescent microspheres conjugated with chlorine e6 in the left IC. (B) Schematic showing the selective ablation of retrogradely labeled layer V corticocollicular neurons by illumination of the ipsilateral auditory cortex with near-infrared light. (C) Sound localization accuracy (averaged across 12 speaker locations in the horizontal plane) before the right ear was plugged (Preplug), on each of the 10 days over which an ear plug was worn and following its removal (Post-plug). Data from control animals are shown in black and from the ferrets with corticocollicular lesions in red. The symbols represent different animals and the lines show the mean scores. (D) Staining with the SMI32 antibody, a marker of layer III and layer V pyramidal cortical neurons, was sparser in the left (lesioned) primary auditory cortex, resulting in a less distinct bilaminar appearance (top) than on the right side (bottom). Calibration bars: 2 mm in (A) and 0.1 mm in (D). Modified with permission from Bajo et al. (2010a).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
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Figure 9: The projection from the auditory cortex to the inferior colliculus is essential for training-induced plasticity of spatial hearing in adult ferrets. (A) Lateral view of the ferret midbrain showing the location and number of injections of fluorescent microspheres conjugated with chlorine e6 in the left IC. (B) Schematic showing the selective ablation of retrogradely labeled layer V corticocollicular neurons by illumination of the ipsilateral auditory cortex with near-infrared light. (C) Sound localization accuracy (averaged across 12 speaker locations in the horizontal plane) before the right ear was plugged (Preplug), on each of the 10 days over which an ear plug was worn and following its removal (Post-plug). Data from control animals are shown in black and from the ferrets with corticocollicular lesions in red. The symbols represent different animals and the lines show the mean scores. (D) Staining with the SMI32 antibody, a marker of layer III and layer V pyramidal cortical neurons, was sparser in the left (lesioned) primary auditory cortex, resulting in a less distinct bilaminar appearance (top) than on the right side (bottom). Calibration bars: 2 mm in (A) and 0.1 mm in (D). Modified with permission from Bajo et al. (2010a).
Mentions: To address this question, Bajo et al. (2010a) used a chromophore-targeted neuronal degeneration technique to investigate the behavioral effects in ferrets of selectively eliminating layer V pyramidal cells in the primary auditory cortical areas that project to the IC (Figure 9). This involved retrogradely labeling corticocollicular projection neurons by injecting fluorescent microbeads conjugated with chlorine e6 in the IC on one side of the brain, and subsequently illuminating the ipsilateral auditory cortex with near-infrared light. This resulted in a loss of about two thirds of the A1 neurons that project to the IC, without affecting those in surrounding cortical areas. As previously discussed, most corticocollicular axons target the ipsilateral IC, so this approach allowed an assessment of the effects of removing descending axons predominantly on one side of the brain only.

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.


Related in: MedlinePlus