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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

Electron micrographs of labeled endings in the three main subdivisions of the IC after a large injection of biotinylated dextran amine was made in the ipsilateral primary auditory cortex in the rat. Labeled terminals in DCIC (A), CNIC (B), and LCIC (C) contain round vesicles and make asymmetric synaptic contacts (arrows). Unlabeled terminals with pleomorphic vesicles are also observed (stars). Inset in panel (A) shows the distribution of corticocollicular terminal fields and the areas (the box in each IC subdivision) that were used for electron microscopy. Calibration bar: 0.4 μm. Modified with permission from Saldaña et al. (1996).
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Figure 5: Electron micrographs of labeled endings in the three main subdivisions of the IC after a large injection of biotinylated dextran amine was made in the ipsilateral primary auditory cortex in the rat. Labeled terminals in DCIC (A), CNIC (B), and LCIC (C) contain round vesicles and make asymmetric synaptic contacts (arrows). Unlabeled terminals with pleomorphic vesicles are also observed (stars). Inset in panel (A) shows the distribution of corticocollicular terminal fields and the areas (the box in each IC subdivision) that were used for electron microscopy. Calibration bar: 0.4 μm. Modified with permission from Saldaña et al. (1996).

Mentions: Only two studies have analyzed the corticollicular terminals at an ultrastructural level. Jones and Rockel (1973) examined degenerated boutons in the IC of cats in which cortical lesions had been made, while Saldaña et al. (1996) labeled terminal boutons in the rat IC after making biotinylated dextran amine injections in A1 (Figure 5). Labeled boutons in every IC subdivision contained round synaptic vesicles and made asymmetric synaptic contacts (Figure 5, arrows), which are generally thought to be features of excitatory synapses (Peters et al., 1991). This is consistent with evidence for the glutamatergic nature of this projection as demonstrated by a decrease in D-aspartate release in the different IC subdivisions following auditory cortex ablation (Feliciano and Potashner, 1995). Corticocollicular fibers synapse mainly on distal dendritic profiles, including dendritic spines, with few contacts on cell bodies or large dendrites (Saldaña et al., 1996).


Cortical modulation of auditory processing in the midbrain.

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

Electron micrographs of labeled endings in the three main subdivisions of the IC after a large injection of biotinylated dextran amine was made in the ipsilateral primary auditory cortex in the rat. Labeled terminals in DCIC (A), CNIC (B), and LCIC (C) contain round vesicles and make asymmetric synaptic contacts (arrows). Unlabeled terminals with pleomorphic vesicles are also observed (stars). Inset in panel (A) shows the distribution of corticocollicular terminal fields and the areas (the box in each IC subdivision) that were used for electron microscopy. Calibration bar: 0.4 μm. Modified with permission from Saldaña et al. (1996).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Electron micrographs of labeled endings in the three main subdivisions of the IC after a large injection of biotinylated dextran amine was made in the ipsilateral primary auditory cortex in the rat. Labeled terminals in DCIC (A), CNIC (B), and LCIC (C) contain round vesicles and make asymmetric synaptic contacts (arrows). Unlabeled terminals with pleomorphic vesicles are also observed (stars). Inset in panel (A) shows the distribution of corticocollicular terminal fields and the areas (the box in each IC subdivision) that were used for electron microscopy. Calibration bar: 0.4 μm. Modified with permission from Saldaña et al. (1996).
Mentions: Only two studies have analyzed the corticollicular terminals at an ultrastructural level. Jones and Rockel (1973) examined degenerated boutons in the IC of cats in which cortical lesions had been made, while Saldaña et al. (1996) labeled terminal boutons in the rat IC after making biotinylated dextran amine injections in A1 (Figure 5). Labeled boutons in every IC subdivision contained round synaptic vesicles and made asymmetric synaptic contacts (Figure 5, arrows), which are generally thought to be features of excitatory synapses (Peters et al., 1991). This is consistent with evidence for the glutamatergic nature of this projection as demonstrated by a decrease in D-aspartate release in the different IC subdivisions following auditory cortex ablation (Feliciano and Potashner, 1995). Corticocollicular fibers synapse mainly on distal dendritic profiles, including dendritic spines, with few contacts on cell bodies or large dendrites (Saldaña et al., 1996).

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