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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

Population response across time and spatial location. Each panel shows the response of the population of A1 (top) and CL (bottom) neurons in young animals (left) and aged animals (right). Warmer colors represent greater activity. The response period is shown as the solid line below each panel. Each neuron was normalized to the best direction at 0 along the y-axis, with leftward eccentricities below and rightward eccentricities above. Young animals showed an increase in spatial tuning between A1 and CL, as shown by less activity beyond about ± 90°. There was also more of a sustained response for the best direction compared to eccentric directions. Aged animals showed broader tuning in general, particularly in area CL, and a more oscillating response over time.
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Figure 2: Population response across time and spatial location. Each panel shows the response of the population of A1 (top) and CL (bottom) neurons in young animals (left) and aged animals (right). Warmer colors represent greater activity. The response period is shown as the solid line below each panel. Each neuron was normalized to the best direction at 0 along the y-axis, with leftward eccentricities below and rightward eccentricities above. Young animals showed an increase in spatial tuning between A1 and CL, as shown by less activity beyond about ± 90°. There was also more of a sustained response for the best direction compared to eccentric directions. Aged animals showed broader tuning in general, particularly in area CL, and a more oscillating response over time.

Mentions: In order to generalize these responses as the population response within a given cortical area and age group we generated population heat maps of the response as a function of stimulus location and time. For each individual neuron, we normalized the location with the highest firing rate to location 0. We then summed the activity of each 1 ms bin for each neuronal recording session across all neurons recorded in that cortical area in young or aged animals, so that each bin across all acoustic directions and time are represented by a minimum of 1000 trials that accrued across recording sessions. Next, we normalized the population response to the peak response in the best direction, and then used colors to represent the normalized activity. The cortical representation of broadband noise across 360° of acoustic space from the population of neurons A1 and CL in young and aged monkeys is summarized in Figure 2, with warmer colors representing higher firing rates. One interesting feature that is clearly apparent when the data are represented in this way is the temporal dynamics of the response between young (left column) and aged animals (right column). Young animals have an initial burst of activity that decreases consistently with time for stimuli at any given location, and a decrease in activity as the location moves away from the best direction. In contrast, in aged animals there are clearly two peaks of activity across locations and at least three at the best direction. This activity also persists longer in the aged animals compared to younger animals. A second obvious qualitative feature is that the responses in young animals are more sustained for the best direction compared to the flanking directions, particularly for CL neurons. In aged animals the sustained activity is not as dependent on the spatial location of the stimulus as in younger animals. A third notable feature is that the latency for this activity is shorter in aged animals compared to younger animals. Finally, there are clear differences in the responses between the first 100 ms and the second 100 ms of the stimulus period, as well as an increase in activity shortly after the stimulus ended.


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)

Population response across time and spatial location. Each panel shows the response of the population of A1 (top) and CL (bottom) neurons in young animals (left) and aged animals (right). Warmer colors represent greater activity. The response period is shown as the solid line below each panel. Each neuron was normalized to the best direction at 0 along the y-axis, with leftward eccentricities below and rightward eccentricities above. Young animals showed an increase in spatial tuning between A1 and CL, as shown by less activity beyond about ± 90°. There was also more of a sustained response for the best direction compared to eccentric directions. Aged animals showed broader tuning in general, particularly in area CL, and a more oscillating response over time.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Population response across time and spatial location. Each panel shows the response of the population of A1 (top) and CL (bottom) neurons in young animals (left) and aged animals (right). Warmer colors represent greater activity. The response period is shown as the solid line below each panel. Each neuron was normalized to the best direction at 0 along the y-axis, with leftward eccentricities below and rightward eccentricities above. Young animals showed an increase in spatial tuning between A1 and CL, as shown by less activity beyond about ± 90°. There was also more of a sustained response for the best direction compared to eccentric directions. Aged animals showed broader tuning in general, particularly in area CL, and a more oscillating response over time.
Mentions: In order to generalize these responses as the population response within a given cortical area and age group we generated population heat maps of the response as a function of stimulus location and time. For each individual neuron, we normalized the location with the highest firing rate to location 0. We then summed the activity of each 1 ms bin for each neuronal recording session across all neurons recorded in that cortical area in young or aged animals, so that each bin across all acoustic directions and time are represented by a minimum of 1000 trials that accrued across recording sessions. Next, we normalized the population response to the peak response in the best direction, and then used colors to represent the normalized activity. The cortical representation of broadband noise across 360° of acoustic space from the population of neurons A1 and CL in young and aged monkeys is summarized in Figure 2, with warmer colors representing higher firing rates. One interesting feature that is clearly apparent when the data are represented in this way is the temporal dynamics of the response between young (left column) and aged animals (right column). Young animals have an initial burst of activity that decreases consistently with time for stimuli at any given location, and a decrease in activity as the location moves away from the best direction. In contrast, in aged animals there are clearly two peaks of activity across locations and at least three at the best direction. This activity also persists longer in the aged animals compared to younger animals. A second obvious qualitative feature is that the responses in young animals are more sustained for the best direction compared to the flanking directions, particularly for CL neurons. In aged animals the sustained activity is not as dependent on the spatial location of the stimulus as in younger animals. A third notable feature is that the latency for this activity is shorter in aged animals compared to younger animals. Finally, there are clear differences in the responses between the first 100 ms and the second 100 ms of the stimulus period, as well as an increase in activity shortly after the stimulus ended.

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