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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

Terminal fields in the IC after a tracer injection in the ferret auditory cortex. (A) Coronal section at the level of the left auditory cortex showing the location of a rhodamine injection site in the center of the MEG where A1 is located. The halo of the injection site is shown in gray while the center is in black. (B–D) Examples of anterograde terminal fields in the IC at the locations indicated by the boxes in (E). Calibration bars: 1 mm (A), 100 μm (B–D), 0.5 mm (E). Modified with permission from Bajo et al. (2007).
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Figure 4: Terminal fields in the IC after a tracer injection in the ferret auditory cortex. (A) Coronal section at the level of the left auditory cortex showing the location of a rhodamine injection site in the center of the MEG where A1 is located. The halo of the injection site is shown in gray while the center is in black. (B–D) Examples of anterograde terminal fields in the IC at the locations indicated by the boxes in (E). Calibration bars: 1 mm (A), 100 μm (B–D), 0.5 mm (E). Modified with permission from Bajo et al. (2007).

Mentions: With these methods, however, it was difficult to demonstrate that the degenerated fibers observed actually terminate in the IC itself, but this was subsequently confirmed using different anterograde neural tracers in a large variety of mammals (tamarin, Luethke et al., 1989; squirrel monkey, Fitzpatrick and Imig, 1978; cat, Andersen et al., 1980; Winer et al., 1998; ferret, Bajo et al., 2007; rat, Coleman and Clerici, 1987; Herrera et al., 1994; Saldaña et al., 1996; gerbil, Budinger et al., 2000). An example of cortical terminal fields in the IC is shown in Figure 4. In this case, a large rhodamine injection was made in ferret A1 (Figure 4A), which produced a symmetrical pattern of terminal labeling in each IC. As expected, the ipsilateral IC was most heavily labeled (Figure 4E). Cortical axons mainly innervated the dorsomedial region of the IC, with terminal fields more profuse in the DCIC than in the dorsal part of the CNIC. The labeled axons in the CNIC were also thinner and their terminals smaller, with lower bouton density, than those in the DCIC (Figures 4C,D). In the lateral cortex (LCIC) of this animal, a network of fibers was observed with many terminals and en passant boutons (Figure 4B).


Cortical modulation of auditory processing in the midbrain.

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

Terminal fields in the IC after a tracer injection in the ferret auditory cortex. (A) Coronal section at the level of the left auditory cortex showing the location of a rhodamine injection site in the center of the MEG where A1 is located. The halo of the injection site is shown in gray while the center is in black. (B–D) Examples of anterograde terminal fields in the IC at the locations indicated by the boxes in (E). Calibration bars: 1 mm (A), 100 μm (B–D), 0.5 mm (E). Modified with permission from Bajo et al. (2007).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Terminal fields in the IC after a tracer injection in the ferret auditory cortex. (A) Coronal section at the level of the left auditory cortex showing the location of a rhodamine injection site in the center of the MEG where A1 is located. The halo of the injection site is shown in gray while the center is in black. (B–D) Examples of anterograde terminal fields in the IC at the locations indicated by the boxes in (E). Calibration bars: 1 mm (A), 100 μm (B–D), 0.5 mm (E). Modified with permission from Bajo et al. (2007).
Mentions: With these methods, however, it was difficult to demonstrate that the degenerated fibers observed actually terminate in the IC itself, but this was subsequently confirmed using different anterograde neural tracers in a large variety of mammals (tamarin, Luethke et al., 1989; squirrel monkey, Fitzpatrick and Imig, 1978; cat, Andersen et al., 1980; Winer et al., 1998; ferret, Bajo et al., 2007; rat, Coleman and Clerici, 1987; Herrera et al., 1994; Saldaña et al., 1996; gerbil, Budinger et al., 2000). An example of cortical terminal fields in the IC is shown in Figure 4. In this case, a large rhodamine injection was made in ferret A1 (Figure 4A), which produced a symmetrical pattern of terminal labeling in each IC. As expected, the ipsilateral IC was most heavily labeled (Figure 4E). Cortical axons mainly innervated the dorsomedial region of the IC, with terminal fields more profuse in the DCIC than in the dorsal part of the CNIC. The labeled axons in the CNIC were also thinner and their terminals smaller, with lower bouton density, than those in the DCIC (Figures 4C,D). In the lateral cortex (LCIC) of this animal, a network of fibers was observed with many terminals and en passant boutons (Figure 4B).

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