In normal ageing, structural and functional changes in the brain lead to an altered processing of... more In normal ageing, structural and functional changes in the brain lead to an altered processing of sensory stimuli and to changes in cognitive functions. The link between changes in sensory processing and cognition is not well understood, but physical fitness is suggested to be beneficial for both. We recorded event-related potentials to somatosensory and auditory stimuli in a passive change detection paradigm from 81 older and 38 young women and investigated their associations with cognitive performance. In older adults also associations to physical fitness were studied. The somatosensory mismatch response was attenuated in older adults and it associated with executive functions. Somatosensory P3a did not show group differences, but in older adults, it associated with physical fitness. Auditory N1 and P2 responses to repetitive stimuli were larger in amplitude in older than in young adults. There were no group differences in the auditory mismatch negativity, but it associated with working memory capacity in young but not in older adults. Our results indicate that in ageing, changes in stimulus encoding and deviance detection are observable in electrophysiological responses to task-irrelevant somatosensory and auditory stimuli, and the higher somatosensory response amplitudes are associated with better executive functions and physical fitness. Normal ageing is accompanied by a degeneration of brain structure 1 and changes in sensory processing, memory , and executive functions 2,3. Age-related atrophy of brain tissue, together with changes in neural transmission , result in a reorganisation of neural circuits and compensatory brain activity, which eventually leads to alterations in cognitive performance 3,4. Since the changes in the nervous system precede those in behaviour, event-related potentials (ERPs) that reflect the brain's sensory-cognitive functions are promising tools to detect early ageing-related cognitive deterioration 5. Mismatch negativity (MMN), which is an automatic ERP response to stimulus changes, indexes cognitive decline in normal ageing as well as in different neuropsychiatric, neurological, and neurodevelopmental disorders 6,7. The MMN is elicited in the oddball condition, where rare deviant stimuli are interspersed with repetitive standard stimuli 8. The change detection the MMN reflects is based on the comparison process between the memory trace formed by the standard stimuli and deviant stimulus input 9. The MMN occurs usually 150–250 ms post-stimulus 8. The MMN was first discovered in the auditory sensory modality 10 , and changes in stimulus intensity, frequency, or location are reflected by the MMN amplitude 9. The MMN has also been demonstrated to respond to changes in somatosensory 11–14 , visual 15,16 , and olfactory 17 stimuli. In the auditory modality, changes in stimulus duration and frequency have primarily been used to study age-related alterations in sensory processing 18. The auditory MMN (aMMN) amplitude to changes in frequency 19–21 and duration 21,22 is attenuated in older adults compared to young adults. The amplitude of aMMN related to changes in stimulus duration and inter-stimulus intervals may be associated with impaired cognitive performance, especially in verbal memory and executive functions 23–25 .
Aging is associated with cognitive decline and alterations in early perceptual processes. Studies... more Aging is associated with cognitive decline and alterations in early perceptual processes. Studies in the auditory and visual sensory modalities have shown that the mismatch negativity [or the mismatch response (MMR)], an event-related potential (ERP) elicited by a deviant stimulus in a background of homogenous events, diminishes with aging and cognitive decline. However, the effects of aging on the somatosensory MMR (sMMR) are not known. In the current study, we recorded ERPs to electrical pulses to different fingers of the left hand in a passive oddball experiment in young (22–36 years) and elderly (66– 95 years) adults engaged in a visual task. The MMR was found to deviants as compared to standards at two latency ranges: 180–220 ms and 250–290 ms post-stimulus onset. At 180– 220 ms, within the young, the MMR was found at medial electrode sites, whereas aged did not show any amplitude difference between the stimulus types at the same latency range. At 250–290 ms, the MMR was evident with attenuated amplitude and narrowed scalp distribution among aged (Fz) compared to young (fronto-centrally and lateral parietal sites). Hence, the results reveal that the somatosensory change detection mechanism is altered in aging. The sMMR can be used as a reliable measure of age-related changes in sensory-cognitive functions.
In normal ageing, structural and functional changes in the brain lead to an altered processing of... more In normal ageing, structural and functional changes in the brain lead to an altered processing of sensory stimuli and to changes in cognitive functions. The link between changes in sensory processing and cognition is not well understood, but physical fitness is suggested to be beneficial for both. We recorded event-related potentials to somatosensory and auditory stimuli in a passive change detection paradigm from 81 older and 38 young women and investigated their associations with cognitive performance. In older adults also associations to physical fitness were studied. The somatosensory mismatch response was attenuated in older adults and it associated with executive functions. Somatosensory P3a did not show group differences, but in older adults, it associated with physical fitness. Auditory N1 and P2 responses to repetitive stimuli were larger in amplitude in older than in young adults. There were no group differences in the auditory mismatch negativity, but it associated with working memory capacity in young but not in older adults. Our results indicate that in ageing, changes in stimulus encoding and deviance detection are observable in electrophysiological responses to task-irrelevant somatosensory and auditory stimuli, and the higher somatosensory response amplitudes are associated with better executive functions and physical fitness. Normal ageing is accompanied by a degeneration of brain structure 1 and changes in sensory processing, memory , and executive functions 2,3. Age-related atrophy of brain tissue, together with changes in neural transmission , result in a reorganisation of neural circuits and compensatory brain activity, which eventually leads to alterations in cognitive performance 3,4. Since the changes in the nervous system precede those in behaviour, event-related potentials (ERPs) that reflect the brain's sensory-cognitive functions are promising tools to detect early ageing-related cognitive deterioration 5. Mismatch negativity (MMN), which is an automatic ERP response to stimulus changes, indexes cognitive decline in normal ageing as well as in different neuropsychiatric, neurological, and neurodevelopmental disorders 6,7. The MMN is elicited in the oddball condition, where rare deviant stimuli are interspersed with repetitive standard stimuli 8. The change detection the MMN reflects is based on the comparison process between the memory trace formed by the standard stimuli and deviant stimulus input 9. The MMN occurs usually 150–250 ms post-stimulus 8. The MMN was first discovered in the auditory sensory modality 10 , and changes in stimulus intensity, frequency, or location are reflected by the MMN amplitude 9. The MMN has also been demonstrated to respond to changes in somatosensory 11–14 , visual 15,16 , and olfactory 17 stimuli. In the auditory modality, changes in stimulus duration and frequency have primarily been used to study age-related alterations in sensory processing 18. The auditory MMN (aMMN) amplitude to changes in frequency 19–21 and duration 21,22 is attenuated in older adults compared to young adults. The amplitude of aMMN related to changes in stimulus duration and inter-stimulus intervals may be associated with impaired cognitive performance, especially in verbal memory and executive functions 23–25 .
Aging is associated with cognitive decline and alterations in early perceptual processes. Studies... more Aging is associated with cognitive decline and alterations in early perceptual processes. Studies in the auditory and visual sensory modalities have shown that the mismatch negativity [or the mismatch response (MMR)], an event-related potential (ERP) elicited by a deviant stimulus in a background of homogenous events, diminishes with aging and cognitive decline. However, the effects of aging on the somatosensory MMR (sMMR) are not known. In the current study, we recorded ERPs to electrical pulses to different fingers of the left hand in a passive oddball experiment in young (22–36 years) and elderly (66– 95 years) adults engaged in a visual task. The MMR was found to deviants as compared to standards at two latency ranges: 180–220 ms and 250–290 ms post-stimulus onset. At 180– 220 ms, within the young, the MMR was found at medial electrode sites, whereas aged did not show any amplitude difference between the stimulus types at the same latency range. At 250–290 ms, the MMR was evident with attenuated amplitude and narrowed scalp distribution among aged (Fz) compared to young (fronto-centrally and lateral parietal sites). Hence, the results reveal that the somatosensory change detection mechanism is altered in aging. The sMMR can be used as a reliable measure of age-related changes in sensory-cognitive functions.
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Papers by Juho Strömmer