Limits...
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.


Anatomical tracing experiments in guinea pigs show that cortical cells project to the IC bilaterally. (A) Coronal section at the level of the right auditory cortex showing the overlay of cells labeled retrogradely by injections of Fast Blue in the right IC and rhodamine microbeads in the left IC, with a higher magnification of the area enclosed by the white box in (B). (C,C') Double-labeled cortical cells (arrowheads) using the same tracer combination. (D,D') A double-labeled cortical cell following an injection of Fast Blue in the ipsilateral IC and fluorescein microbeads in the contralateral IC. Arrowheads indicate double labeled cells. Calibration bars: 0.5 mm (A) and 20 μm (B–D). Modified with permission from Coomes et al. (2005).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3539853&req=5

Figure 2: Anatomical tracing experiments in guinea pigs show that cortical cells project to the IC bilaterally. (A) Coronal section at the level of the right auditory cortex showing the overlay of cells labeled retrogradely by injections of Fast Blue in the right IC and rhodamine microbeads in the left IC, with a higher magnification of the area enclosed by the white box in (B). (C,C') Double-labeled cortical cells (arrowheads) using the same tracer combination. (D,D') A double-labeled cortical cell following an injection of Fast Blue in the ipsilateral IC and fluorescein microbeads in the contralateral IC. Arrowheads indicate double labeled cells. Calibration bars: 0.5 mm (A) and 20 μm (B–D). Modified with permission from Coomes et al. (2005).

Mentions: In the following decades, corticocollicular projections were described in squirrel monkeys (Winer et al., 2002), cats (Kelly and Wong, 1981; Winer and Prieto, 2001), ferrets (Bajo et al., 2007), guinea pigs (Strutz, 1987; Coomes et al., 2005), rats (Druga and Syka, 1984; Games and Winer, 1988; Herbert et al., 1991), gerbils (Bajo and Moore, 2005), and even in Madagascan tenrecs (Künzle, 1995). The use of modern retrograde tracers has confirmed that projection neurons that target the IC are found in layer V of the auditory cortex layer (Figures 1A,B and 2A) and revealed much about the morphology of these neurons (Figures 1–3).


Cortical modulation of auditory processing in the midbrain.

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

Anatomical tracing experiments in guinea pigs show that cortical cells project to the IC bilaterally. (A) Coronal section at the level of the right auditory cortex showing the overlay of cells labeled retrogradely by injections of Fast Blue in the right IC and rhodamine microbeads in the left IC, with a higher magnification of the area enclosed by the white box in (B). (C,C') Double-labeled cortical cells (arrowheads) using the same tracer combination. (D,D') A double-labeled cortical cell following an injection of Fast Blue in the ipsilateral IC and fluorescein microbeads in the contralateral IC. Arrowheads indicate double labeled cells. Calibration bars: 0.5 mm (A) and 20 μm (B–D). Modified with permission from Coomes et al. (2005).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Anatomical tracing experiments in guinea pigs show that cortical cells project to the IC bilaterally. (A) Coronal section at the level of the right auditory cortex showing the overlay of cells labeled retrogradely by injections of Fast Blue in the right IC and rhodamine microbeads in the left IC, with a higher magnification of the area enclosed by the white box in (B). (C,C') Double-labeled cortical cells (arrowheads) using the same tracer combination. (D,D') A double-labeled cortical cell following an injection of Fast Blue in the ipsilateral IC and fluorescein microbeads in the contralateral IC. Arrowheads indicate double labeled cells. Calibration bars: 0.5 mm (A) and 20 μm (B–D). Modified with permission from Coomes et al. (2005).
Mentions: In the following decades, corticocollicular projections were described in squirrel monkeys (Winer et al., 2002), cats (Kelly and Wong, 1981; Winer and Prieto, 2001), ferrets (Bajo et al., 2007), guinea pigs (Strutz, 1987; Coomes et al., 2005), rats (Druga and Syka, 1984; Games and Winer, 1988; Herbert et al., 1991), gerbils (Bajo and Moore, 2005), and even in Madagascan tenrecs (Künzle, 1995). The use of modern retrograde tracers has confirmed that projection neurons that target the IC are found in layer V of the auditory cortex layer (Figures 1A,B and 2A) and revealed much about the morphology of these neurons (Figures 1–3).

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.