Limits...
Neural circuits underlying adaptation and learning in the perception of auditory space.

King AJ, Dahmen JC, Keating P, Leach ND, Nodal FR, Bajo VM - Neurosci Biobehav Rev (2011)

Bottom Line: Sound localization mechanisms are particularly plastic during development, when the monaural and binaural acoustic cues that form the basis for spatial hearing change in value as the body grows.Recent studies have shown that the mature brain retains a surprising capacity to relearn to localize sound in the presence of substantially altered auditory spatial cues.Through a combination of recording studies and methods for selectively manipulating the activity of specific neuronal populations, progress is now being made in identifying the cortical and subcortical circuits in the brain that are responsible for the dynamic coding of auditory spatial information.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Anatomy and Genetics, Sherrington Building, University of Oxford, Parks Road, Oxford, UK. andrew.king@dpag.ox.ac.uk

Show MeSH
Loss of cholinergic input from the nucleus basalis to the auditory cortex appears to disrupt learning-induced plasticity. The number of AChEase fibers in the auditory cortex (A) and of the low affinity neurotrophin receptor (p75NTR) positive cells in the nucleus basalis (B) was significantly lower following injections of the immunotoxin ME20.4-SAP in the ipsilateral auditory cortex. ME20.4-SAP comprises a monoclonal antibody specific for the p75NTR membrane-bound receptor, conjugated to saporin, a ribosome-inactivating enzyme. Once bound to the external cell membrane, the saporin toxin is internalized and prevents protein synthesis, resulting in neuronal cell death. The p75NTR receptor is primarily expressed by the cholinergic cells of the basal forebrain and, after being injected into the auditory cortex, ME20.4-SAP is taken up only by cortical cholinergic afferents. (C) The ability to adapt to altered spatial cues caused by the monaural insertion of an earplug was reduced in ferrets in which cholinergic innervation to the cortex had been compromised by this method. Abbreviations: I to VI, layers of the cortex; Cl, claustrum; D, dorsal; ic, internal capsule; L, lateral; NB, nucleus basalis; ps, pial surface; wm, white matter.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3198863&req=5

fig0025: Loss of cholinergic input from the nucleus basalis to the auditory cortex appears to disrupt learning-induced plasticity. The number of AChEase fibers in the auditory cortex (A) and of the low affinity neurotrophin receptor (p75NTR) positive cells in the nucleus basalis (B) was significantly lower following injections of the immunotoxin ME20.4-SAP in the ipsilateral auditory cortex. ME20.4-SAP comprises a monoclonal antibody specific for the p75NTR membrane-bound receptor, conjugated to saporin, a ribosome-inactivating enzyme. Once bound to the external cell membrane, the saporin toxin is internalized and prevents protein synthesis, resulting in neuronal cell death. The p75NTR receptor is primarily expressed by the cholinergic cells of the basal forebrain and, after being injected into the auditory cortex, ME20.4-SAP is taken up only by cortical cholinergic afferents. (C) The ability to adapt to altered spatial cues caused by the monaural insertion of an earplug was reduced in ferrets in which cholinergic innervation to the cortex had been compromised by this method. Abbreviations: I to VI, layers of the cortex; Cl, claustrum; D, dorsal; ic, internal capsule; L, lateral; NB, nucleus basalis; ps, pial surface; wm, white matter.

Mentions: Recent work in ferrets has investigated the involvement of cholinergic neuromodulation in the ability of adult ferrets to localize sounds in space and to adapt to the altered spatial cues produced by plugging one ear (Leach et al., 2011). Fig. 5 shows a single case with multiple injections of a specific neurotoxin throughout the left auditory cortex, from where it is transported retrogradely back to the NB and induces cell death. This produced a substantial decrease (of around 70%) in both the number of cholinergic (p75NTR immunopositive) cells in the ipsilateral NB and acetylcholinesterase-positive fibers in A1 on that side of the brain (Fig. 5A and B). Behaviorally, these cholinergic lesions produced a modest impairment in the localization of brief sounds (40–100 ms in duration), as shown by the lower percentage of correct scores and higher error rates compared with control animals. Interestingly, no differences in performance were observed between the left and right hemifields, as might be anticipated from unilateral cortical lesions, a result which might indicate a more global role for acetylcholine. Indeed, McGaughy and colleagues have shown that impairments in cortical cholinergic transmission produce substantial deficits in sustained attention and stimulus detection thresholds during a visual discrimination task (McGaughy et al., 1996; McGaughy and Sarter, 1998). The capacity of the ferrets to relearn to localize sound accurately in the presence of a unilateral hearing loss was also slightly reduced compared to controls (Fig. 5C), indicating a likely role for the cholinergic system in auditory spatial learning.


Neural circuits underlying adaptation and learning in the perception of auditory space.

King AJ, Dahmen JC, Keating P, Leach ND, Nodal FR, Bajo VM - Neurosci Biobehav Rev (2011)

Loss of cholinergic input from the nucleus basalis to the auditory cortex appears to disrupt learning-induced plasticity. The number of AChEase fibers in the auditory cortex (A) and of the low affinity neurotrophin receptor (p75NTR) positive cells in the nucleus basalis (B) was significantly lower following injections of the immunotoxin ME20.4-SAP in the ipsilateral auditory cortex. ME20.4-SAP comprises a monoclonal antibody specific for the p75NTR membrane-bound receptor, conjugated to saporin, a ribosome-inactivating enzyme. Once bound to the external cell membrane, the saporin toxin is internalized and prevents protein synthesis, resulting in neuronal cell death. The p75NTR receptor is primarily expressed by the cholinergic cells of the basal forebrain and, after being injected into the auditory cortex, ME20.4-SAP is taken up only by cortical cholinergic afferents. (C) The ability to adapt to altered spatial cues caused by the monaural insertion of an earplug was reduced in ferrets in which cholinergic innervation to the cortex had been compromised by this method. Abbreviations: I to VI, layers of the cortex; Cl, claustrum; D, dorsal; ic, internal capsule; L, lateral; NB, nucleus basalis; ps, pial surface; wm, white matter.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3198863&req=5

fig0025: Loss of cholinergic input from the nucleus basalis to the auditory cortex appears to disrupt learning-induced plasticity. The number of AChEase fibers in the auditory cortex (A) and of the low affinity neurotrophin receptor (p75NTR) positive cells in the nucleus basalis (B) was significantly lower following injections of the immunotoxin ME20.4-SAP in the ipsilateral auditory cortex. ME20.4-SAP comprises a monoclonal antibody specific for the p75NTR membrane-bound receptor, conjugated to saporin, a ribosome-inactivating enzyme. Once bound to the external cell membrane, the saporin toxin is internalized and prevents protein synthesis, resulting in neuronal cell death. The p75NTR receptor is primarily expressed by the cholinergic cells of the basal forebrain and, after being injected into the auditory cortex, ME20.4-SAP is taken up only by cortical cholinergic afferents. (C) The ability to adapt to altered spatial cues caused by the monaural insertion of an earplug was reduced in ferrets in which cholinergic innervation to the cortex had been compromised by this method. Abbreviations: I to VI, layers of the cortex; Cl, claustrum; D, dorsal; ic, internal capsule; L, lateral; NB, nucleus basalis; ps, pial surface; wm, white matter.
Mentions: Recent work in ferrets has investigated the involvement of cholinergic neuromodulation in the ability of adult ferrets to localize sounds in space and to adapt to the altered spatial cues produced by plugging one ear (Leach et al., 2011). Fig. 5 shows a single case with multiple injections of a specific neurotoxin throughout the left auditory cortex, from where it is transported retrogradely back to the NB and induces cell death. This produced a substantial decrease (of around 70%) in both the number of cholinergic (p75NTR immunopositive) cells in the ipsilateral NB and acetylcholinesterase-positive fibers in A1 on that side of the brain (Fig. 5A and B). Behaviorally, these cholinergic lesions produced a modest impairment in the localization of brief sounds (40–100 ms in duration), as shown by the lower percentage of correct scores and higher error rates compared with control animals. Interestingly, no differences in performance were observed between the left and right hemifields, as might be anticipated from unilateral cortical lesions, a result which might indicate a more global role for acetylcholine. Indeed, McGaughy and colleagues have shown that impairments in cortical cholinergic transmission produce substantial deficits in sustained attention and stimulus detection thresholds during a visual discrimination task (McGaughy et al., 1996; McGaughy and Sarter, 1998). The capacity of the ferrets to relearn to localize sound accurately in the presence of a unilateral hearing loss was also slightly reduced compared to controls (Fig. 5C), indicating a likely role for the cholinergic system in auditory spatial learning.

Bottom Line: Sound localization mechanisms are particularly plastic during development, when the monaural and binaural acoustic cues that form the basis for spatial hearing change in value as the body grows.Recent studies have shown that the mature brain retains a surprising capacity to relearn to localize sound in the presence of substantially altered auditory spatial cues.Through a combination of recording studies and methods for selectively manipulating the activity of specific neuronal populations, progress is now being made in identifying the cortical and subcortical circuits in the brain that are responsible for the dynamic coding of auditory spatial information.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, Anatomy and Genetics, Sherrington Building, University of Oxford, Parks Road, Oxford, UK. andrew.king@dpag.ox.ac.uk

Show MeSH