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Characterizing spatial tuning functions of neurons in the auditory cortex of young and aged monkeys: a new perspective on old data.

Engle JR, Recanzone GH - Front Aging Neurosci (2013)

Bottom Line: It is also possible that spatial tuning was decreased as a consequence of reduced inhibition at non-best locations.In this report we found that aged animals had greater activity throughout the response period, but primarily during the onset of the response.These results can be interpreted in the context of a failure of the timing and efficiency of feed-forward thalamo-cortical and cortico-cortical circuits in aged animals.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology and Center for Neuroscience, University of California at Davis Davis, CA, USA ; Evelyn F. McKnight Brain Institute and ARL Division of Neural Systems, Memory and Aging, University of Arizona Tucson, AZ, USA.

ABSTRACT
Age-related hearing deficits are a leading cause of disability among the aged. While some forms of hearing deficits are peripheral in origin, others are centrally mediated. One such deficit is the ability to localize sounds, a critical component for segregating different acoustic objects and events, which is dependent on the auditory cortex. Recent evidence indicates that in aged animals the normal sharpening of spatial tuning between neurons in primary auditory cortex to the caudal lateral field does not occur as it does in younger animals. As a decrease in inhibition with aging is common in the ascending auditory system, it is possible that this lack of spatial tuning sharpening is due to a decrease in inhibition at different periods within the response. It is also possible that spatial tuning was decreased as a consequence of reduced inhibition at non-best locations. In this report we found that aged animals had greater activity throughout the response period, but primarily during the onset of the response. This was most prominent at non-best directions, which is consistent with the hypothesis that inhibition is a primary mechanism for sharpening spatial tuning curves. We also noted that in aged animals the latency of the response was much shorter than in younger animals, which is consistent with a decrease in pre-onset inhibition. These results can be interpreted in the context of a failure of the timing and efficiency of feed-forward thalamo-cortical and cortico-cortical circuits in aged animals. Such a mechanism, if generalized across cortical areas, could play a major role in age-related cognitive decline.

No MeSH data available.


Related in: MedlinePlus

Percentage of neurons inhibited during different periods of the response. Very few cells showed inhibition during the early period of aged monkeys in both A1 and CL (Panel A) compared to younger animals. Similar results were seen for the late period (B) and the off period (C).
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Figure 7: Percentage of neurons inhibited during different periods of the response. Very few cells showed inhibition during the early period of aged monkeys in both A1 and CL (Panel A) compared to younger animals. Similar results were seen for the late period (B) and the off period (C).

Mentions: This result across the population could be due to all neurons showing inhibitory activity in aged animals, or that there is a larger subset of inhibited neurons in aged animals. To investigate this we compared the percent of inhibited neurons in area A1 and CL of young and aged monkeys. Inhibitory responses were defined as driven firing rates during the early, late, and off that were less than the recorded spontaneous rate (Recanzone, 2000). Figure 7 illustrates the percentage of neurons inhibited in areas A1 and CL of young and aged monkeys as a function of degrees from the best direction during the early, late, and off response periods. In young monkeys, the percentage of neurons inhibited varied as a function of response period and degrees from the best direction. Regardless of the response period, the percent of inhibited responses increased as a function of degrees from the best direction. However, the percentage of inhibited responses in aged monkeys followed a slightly different pattern across the early, late, and off response periods in A1 and CL. We found a significant age-related decline for all directions in A1 (gray vs. black circles) during the early and off periods (χ2, p < 0.05), with only two locations showing a significant decline during the late period (157.5 and 180°). A similar result was seen in CL (gray vs. black squares), although there were more locations that did not show a significant age-related difference (early period, 0°, 22.5°, 45°; late period, −22.5°, 0°, 22.5°, 67.5°, 90°, 112.5°, 135°, 157.5°, 180°; off period, −22.5°, 0°, 22.5°, 45°, 67.5°). This finding indicates that there is much less inhibitory activity in aged A1 and CL neurons during the early period compared to younger animals, but also that inhibitory activity during the late and offset periods is more prevalent than during the early period in both groups of monkeys. These results indicate that younger animals show more neurons that are inhibited across directions and periods compared to aged animals.


Characterizing spatial tuning functions of neurons in the auditory cortex of young and aged monkeys: a new perspective on old data.

Engle JR, Recanzone GH - Front Aging Neurosci (2013)

Percentage of neurons inhibited during different periods of the response. Very few cells showed inhibition during the early period of aged monkeys in both A1 and CL (Panel A) compared to younger animals. Similar results were seen for the late period (B) and the off period (C).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3539457&req=5

Figure 7: Percentage of neurons inhibited during different periods of the response. Very few cells showed inhibition during the early period of aged monkeys in both A1 and CL (Panel A) compared to younger animals. Similar results were seen for the late period (B) and the off period (C).
Mentions: This result across the population could be due to all neurons showing inhibitory activity in aged animals, or that there is a larger subset of inhibited neurons in aged animals. To investigate this we compared the percent of inhibited neurons in area A1 and CL of young and aged monkeys. Inhibitory responses were defined as driven firing rates during the early, late, and off that were less than the recorded spontaneous rate (Recanzone, 2000). Figure 7 illustrates the percentage of neurons inhibited in areas A1 and CL of young and aged monkeys as a function of degrees from the best direction during the early, late, and off response periods. In young monkeys, the percentage of neurons inhibited varied as a function of response period and degrees from the best direction. Regardless of the response period, the percent of inhibited responses increased as a function of degrees from the best direction. However, the percentage of inhibited responses in aged monkeys followed a slightly different pattern across the early, late, and off response periods in A1 and CL. We found a significant age-related decline for all directions in A1 (gray vs. black circles) during the early and off periods (χ2, p < 0.05), with only two locations showing a significant decline during the late period (157.5 and 180°). A similar result was seen in CL (gray vs. black squares), although there were more locations that did not show a significant age-related difference (early period, 0°, 22.5°, 45°; late period, −22.5°, 0°, 22.5°, 67.5°, 90°, 112.5°, 135°, 157.5°, 180°; off period, −22.5°, 0°, 22.5°, 45°, 67.5°). This finding indicates that there is much less inhibitory activity in aged A1 and CL neurons during the early period compared to younger animals, but also that inhibitory activity during the late and offset periods is more prevalent than during the early period in both groups of monkeys. These results indicate that younger animals show more neurons that are inhibited across directions and periods compared to aged animals.

Bottom Line: It is also possible that spatial tuning was decreased as a consequence of reduced inhibition at non-best locations.In this report we found that aged animals had greater activity throughout the response period, but primarily during the onset of the response.These results can be interpreted in the context of a failure of the timing and efficiency of feed-forward thalamo-cortical and cortico-cortical circuits in aged animals.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology and Center for Neuroscience, University of California at Davis Davis, CA, USA ; Evelyn F. McKnight Brain Institute and ARL Division of Neural Systems, Memory and Aging, University of Arizona Tucson, AZ, USA.

ABSTRACT
Age-related hearing deficits are a leading cause of disability among the aged. While some forms of hearing deficits are peripheral in origin, others are centrally mediated. One such deficit is the ability to localize sounds, a critical component for segregating different acoustic objects and events, which is dependent on the auditory cortex. Recent evidence indicates that in aged animals the normal sharpening of spatial tuning between neurons in primary auditory cortex to the caudal lateral field does not occur as it does in younger animals. As a decrease in inhibition with aging is common in the ascending auditory system, it is possible that this lack of spatial tuning sharpening is due to a decrease in inhibition at different periods within the response. It is also possible that spatial tuning was decreased as a consequence of reduced inhibition at non-best locations. In this report we found that aged animals had greater activity throughout the response period, but primarily during the onset of the response. This was most prominent at non-best directions, which is consistent with the hypothesis that inhibition is a primary mechanism for sharpening spatial tuning curves. We also noted that in aged animals the latency of the response was much shorter than in younger animals, which is consistent with a decrease in pre-onset inhibition. These results can be interpreted in the context of a failure of the timing and efficiency of feed-forward thalamo-cortical and cortico-cortical circuits in aged animals. Such a mechanism, if generalized across cortical areas, could play a major role in age-related cognitive decline.

No MeSH data available.


Related in: MedlinePlus