studies of memory and aging suggest that some functions are impaired in the elderly , whereas other functions are altered only slightly or not at all . normal age - associated memory decline is not uniform and some cognitive changes are likely to begin in early adulthood . the previous literature on cross - sectional and longitudinal studies suggests that subtle memory changes can begin as early as the early or middle twenties and continue to decline linearly with age [ 2 , 3 ] . short - term memory ( stm ) , for example , appears to remain relatively stable until about the age of 70 , at which point it begins to drop [ 3 , 4 ] . furthermore , normal aging is associated with decline of cognitive performance [ 1 , 5 ] , and these age - related alterations are linked to changes in brain structure and function . one example of the alteration in brain structure and function is a compensatory right side activation in older adults for tasks that are normally left - side lateralized in young adults . this is thought to be related with age - related cognitive decline which affects the right hemisphere more than the left hemisphere . the effect is proposed to be due to grey / white matter ratio which is greater in the left compared to the right hemisphere [ 6 , 7 ] . furthermore , research on white matter and grey matter loss during healthy aging also reported a 3%5% linear reduction per decade in brain areas . using the voxel - based morphometry ( vbm ) approach , several magnetic resonance imaging ( mri ) studies have reported a consistent pattern of age - related grey matter volumetric reductions in the human neocortex , involving temporal association cortices ; these include the superior temporal gyrus ( stg ) and heschl 's gyrus ( hg ) [ 911 ] . in addition , there have been relatively consistent reports of age - related grey matter changes in the cerebellum , basal ganglia , and thalamus [ 1215 ] . good et al .   found a linear decline in global grey matter volume with age and several focal areas of relatively greater age - associated loss . the reduction in grey matter and white matter volume will contribute to decline in cognitive processing . age - related declines are thought to undergo a series of deleterious changes which are thought to lead to deficits in cognitive processing including both increases and decreases in brain activity compared to that in the younger , less - impaired brain . thus , it is important to evaluate these brain areas during cognitive tasks given their sensitivity to aging . additionally , healthy aging causes chemical and physiological changes which are suggested to contribute to the reorganization of the brain function [ 16 , 18 ] . this reorganization of the brain may also be explained with the decline - compensation hypothesis . this hypothesis states that the aging brain will underrecruit task - relevant brain regions and recruit additional cortical resources compared to younger brain . underrecruitment should be a dominant outcome if aging reduces the hemodynamic response or alters its coupling to neural activity . moreover , additional recruitment of brain areas in older adults suggests that the proper cognitive strategy is used to modify the effects of aging . in cortical processing of auditory stimuli , the most common problem in aged people is related to the difficulty in discriminating speech sounds in noisy environments [ 21 , 22 ] . this is particularly problematic given that most speech interactions in everyday conditions occur in noisy backgrounds [ 17 , 23 , 24 ] . this is presumably due to mechanisms involved in suppression of irrelevant information and concentration on the task [ 25 , 26 ] . older adults are more distracted by novel irrelevant sounds than younger adults , indicating deterioration to the cognitive and auditory processes in relation to aging . in order to assess age - related decline in cognitive performance , a forward repeat span task ( frt ) this task was adapted from that described by light and anderson , designed to investigate short - term memory ( stm ) capacity [ 28 , 29 ] . frt was used due to its involvement in cognitive processes that require the involvement of stm and attention processes . the use of a verbal form of frt enables an investigation on both auditory and stm processing . the present study tests two hypotheses by examining stm task in quiet and in 5  db snr on four groups of participants with age range between 20 and 65 years . if a mature human brain is capable of retaining a great deal of plasticity , it raises the possibility that cortical reorganization may occur during normal aging , and we might expect to see compensation or overrecruitment of contralateral brain areas which are not activated or less activated in the younger group . secondly , if the presence of 5  db snr background noise severely affects brain reorganization processes compared to that in the quiet background , we might expect to see compensation or overrecruitment of contralateral areas occurring earlier compared to that in quiet . fifty - one malay male right - handed adults ( as indicated by the edinburgh inventory )   with age range of 20 to 29 years ( mean 27 years , sd 2.18 ) , 30 to 39 years ( mean 33 years , sd 2.18 ) , 40 to 49 years ( mean 45 years , sd 2.28 ) , and 50 to 65 ( mean 59 years , sd 2.49 ) ( as in table 1 ) participated in this study . all participants were native malay speakers and reported no history of psychiatric or neurological disorders and no current use of any psychoactive medications . each participant 's health status was examined through an interview prior to the experiment . from self - report assessment , the older adults ( group 50 and above ) were also given the mini - mental status examination ( mmse )   and all of them scored in the normal range between 28 and 30 . after full explanation of the nature and risks of the study , informed consent was obtained according to the protocol approved by the institutional ethics committee ( iec ) of universiti kebangsaan malaysia . functional mri scans were conducted in the department of radiology , ukm medical centre , using a 1.5 tesla magnetic resonance imaging ( mri ) system ( siemens avanto ) equipped with functional imaging options and echo planar imaging capabilities . a radiofrequency ( rf ) head coil was used for signal transmission and reception . t1-weighted multiplanar reconstruction ( mpr ) spin - echo pulse sequence was collected with the following parameters : tr = 1240  ms , fov = 250  mm 250  mm , flip angle = 90 , matrix size = 128  128 , and slice thickness = 1  mm . functional images were then acquired using a gradient echo - echo planar imaging ( gre - epi ) pulse sequence . each whole brain acquisition consisted of 21 axial slices , which comprised all brain regions including the cerebellum . the following parameters were used : repetition time ( tr ) = 2000  ms , echo time ( te ) = 50  ms , field of view ( fov ) = 192  192  mm , flip angle (  ) = 90 , matrix size = 128  128 , and slice thickness = 5  mm with 1.25  mm gap . a sparse imaging paradigm was used to avoid the interference of scanner sound with the stimulus . stimuli consisted of series of natural speech words produced by a malay male adult voice and were digitally recorded ( sony digital voice editor ) , stored , and edited ( adobe audition 2.0 ) . the multitalker babble noise stimulus was originally recorded from five volunteers reading different passages simultaneously and was edited so that the intensity level was 50  db . the intensity level of the short - term memory task in quiet ( stmq ) was 55  db . for the short - term memory task in babble noise ( stmn ) , the signal - to - noise ratio ( snr ) was 5  db throughout the presentation . the paradigm and procedure of the present study were similar to that in our previous published study . as in figure 1(a ) , there were 120 trials in total with 16 s duration for each trial . there were four experimental conditions : ( i ) 20 trials listening to babble noise ( n ) , ( ii ) 20 trials performing stm task in 5  db snr ( stmn ) , ( iii ) 20 trials performing stm task in quiet ( stmq ) , and ( iv ) 60 rest with no stimuli ( q ) . the sequence of conditions used during the study was fixed , n - q - stmn - q - stmq - q - n , for the primary reason that reaction time is faster when using fixed sequences . a total of 40 ( 2-syllable and 3-syllable ) verbs and nouns which were unrelated familiar malay words were randomized to produce 40-trial sets . five consecutive stimuli each with 0.6  s duration separated by 0.5  s silent gap made up a 5  s stimulus train . during a trial , the stimuli were presented at the 6th second and lasted approximately 5  s. for stmq and stmn conditions , participants were instructed to repeat forward all the words presented .   before a participant entered the fmri scanner , instructions about the task were explained in detail , and instructions were to focus with an otherwise clear mind throughout the procedure and to keep still . during scanning , participants lay comfortably in a supine position in the mr scanner . an adjusted head holder restricted head movement . auditory stimuli were presented through earphones . during scanning , for stmq and stmn conditions , participants were given 5  s to repeat forward aloud all the words . each individual participant 's scores were recorded manually by an experimenter in the console room ( i.e. , number of correct forward repetition trials ) . behavioural results on the forward repeat task ( frt ) with background noise ( 5  db snr ) and without noise were analysed in terms of performance accuracy . paired t - tests were used to analyse the effects of noise on the frt performance for all participants . anova with tukey 's post hoc analysis was used to assess differences in behavioural performance on four groups of participants . finally , linear regression analysis was used to assess the pattern of behavioural performance in association with aging in the different groups . to derive activation maps corresponding to the different tasks , our sparse - imaging data were analysed in a manner similar to procedures in our previous published study . , ma , usa ) and statistical parametric mapping ( spm8 ) ( functional imaging laboratory , wellcome department of imaging neuroscience , institute of neurology , university college of london , uk ; http://www.fil.ion.ucl.ac.uk/spm/ ) . the first two images of every epi - recording session were discarded to account for the approach to steady state in the mr signal . prior to image analysis , each participant 's raw data of fmri scan were motion - corrected and normalized , similar to the previous study . data were further analysed using a 12 parameter nonlinear normalization into the mni - reference state as implemented in spm8 , and with smoothing ( fwhm = 6  mm ) . the fmri data were analysed according to the general linear model as implemented in spm8 . with regard to the different conditions , three regressors were included in the design : ( i ) stmq , ( ii ) stmn , and ( iii ) n. the regressors were convolved using the hemodynamic response function as provided in spm8 . statistical analysis was performed using a mixed effects model ; fixed effects analysis was used for single participant analysis and random effects analysis for group analysis . for group analysis , contrast images were computed for each participant , and then one - sample t - tests were performed . a cortical brain region is regarded as significantly activated only if a minimum cluster size of 10 voxels was reached at a corrected value pfwecorr < 0.001 . voxels or clusters with t values higher than 3.5 were included in the region - of - interest ( roi ) analysis using wfu pickatlas . in each participant , the activated voxels in each of the rois were collected and used to derive the activated volume for each condition for further analysis . activated volumes in the anatomically defined roi were compared between tasks ( stm in quiet and in 5  db snr ) using paired t - tests and between groups using anova . to test whether activation in regions with significant age - related differences is functionally relevant to the tasks in all groups of participants , a correlation analysis between activated volume and the accuracy in behavioural performance was performed .   the laterality index ( li ) was calculated using the formula li = ( vl  vr)/(vl + vr ) , in which vl is the number of the activated voxels in the left hemisphere , and vr is the number of activated voxels in the right hemisphere . the li ranges from 1 to 1 , with 1 to 0 indicating right hemisphere dominance and 0 to 1 indicating left hemisphere dominance . anova analysis ( spss 20.0 statistical software package ) was used to investigate significant main effects ( 2029 year old , group 1 ; 3039 year old , group 2 ; 4049 year old , group 3 ; and 5065 year old , group 4 ) on the forward repeat task ( frt ) ( in quiet and in 5  db snr ) . analyses on noise and in 5  db snr were conducted separately and are shown in table 1 . the effects indicated that neither conditions revealed a significant [ effect of group ] ( p < 0.05 ) . a paired t - test was conducted to examine if the mean frt in quiet and in noise in all groups of participants would differ . the result revealed that the effect of noise on frt was only significant in participants in group 4 ( p = 0.001 , t = 4.533 ) ; other groups showed no significant differences ( all p < 0.05 ) . these results suggest that through the adjustment of the test parameter , task difficulty was reasonably matched for the four age groups . therefore any differences between groups on the imaging data are more likely due to the effects of aging than to differences in task difficulty . the primary goal of the present study was to explore brain activity and the tendency for a laterality shift in four groups of participants performing a short - term memory task in noise ( stmn ) and in quiet ( stmq ) , in relation to healthy aging . the activated volumes of each age group for each task are given in table 2 ( listening to babble noise ) , table 3 ( stmq ) , and table 4 ( stmn ) . to examine the specific differences in activation between stmq and stmn , t - tests were used to compare the activated volume of a given region of interest ( roi ) in each participant ( p < 0.05 ) . the results show no significant differences in brain activity between stmq and stmn in any age group . the laterality index was used to calculate the brain laterality in all tasks ( listening to babble noise , stmq , and stmn ) in all four groups of participants . brain areas which are normally leftward asymmetries in young adults during the short - term memory task change to rightward asymmetries in older participants . the brain areas showing such effects include the superior temporal gyrus ( stg ) , heschl 's gyrus ( hg ) , and cerebellum . in contrast , other activated areas including the middle temporal gyrus ( mtg ) , precentral gyrus ( pcg ) , and postcentral gyri ( post - cg ) remain stable during aging . results also indicate that the laterality shift varies from one region to another ; stg , for example , shows late shifting while cerebellum shows an early shift . n condition was used to evaluate the activation pattern on auditory processing during n task in normal aging brain . table 2 tabulates the number of activated voxels ( nov ) , coordinates of maximum intensity , and the t values of a second - level random effects analysis on four groups of participants . significant activation in bilateral stg ( group 1 : left t = 6.06 , right t = 5.09 ; group 2 : left t = 6.79 , right t = 6.52 ; group 3 : left t = 8.42 , right t = 10.33 ; group 4 : left t = 7.00 , right t = 9.27 ) and mtg ( group 1 : left t = 6.6 , right t = 5.22 ; group 2 : left t = 5.92 , right t = 4.69 ; group 3 : left t = 7.56 , right t = 8.91 ; group 4 : left t = 6.1 , right t = 6.24 ) was observed . results of the laterality index show that there is shifting in brain laterality during aging . this shifting shows left hemisphere dominance in the younger group and right hemisphere dominance in the older group . both stg and mtg show that the laterality shifting starts in group 3 , suggesting its role in compensating for deficits in cognitive processing during aging . comparison between stmq and stmn in all groups of participants reveals that there is no significant difference in brain activity in all groups of participants ( tables 3 and 4 ) ; group 1 ( p = 0.194 , t = 1.382 ) , group 2 ( p = 0.112 , t = 1.728 ) , group 3 ( p = 0.939 , t = 0.078 ) , and group 4 ( p = 0.349 , t = 0.978 ) . results on the laterality index demonstrate that there is reorganization of brain laterality in both stmq and stmn , leftward asymmetries in young group which change to rightward asymmetries in the older group . areas involved in this change are the stg , cerebellum , hg , and pcg . the result also reveals that these laterality shifts vary from one region to another . in stmq , results indicate that stg ( group 1 : left t = 6.61 , right t = 7.23 ; group 2 : left t = 13.13 , right t = 12.45 , group 3 : left t = 12.72 , right t = 14.3 ; group 4 : left t = 6.04 , right t = 8.11 ) starts to become more rightward asymmetries in group 4 . however , for stg in stmn ( group 1 : left t = 5.78 , right t = 5.73 ; group 2 : left t = 12.98 , right t = 11.39 ; group 3 : left t = 18.25 , right t = 12.69 ; group 4 : left t = 8.47 , right t = 7.46 ) , the laterality shift starts earlier ( group 3 ) . for the cerebellum , during stmq ( group 1 : left t = 5.34 , right t = 6.4 ; group 2 : left t = 8.18 , right t = 9.69 ; group 3 : left t = 10.23 , right t = 8.86 ; group 4 : left t = 7.00 , right t = 4.59 ) and stmn ( group 1 : left t = 5.04 , right t = 5.61 ; group 2 : left t = 10.14 , right t = 11.63 ; group 3 : left t = 6.41 , right t = 7.39 : group 4 : left t = 7.00 , right t = 5.89 ) , the changes in hemisphere laterality start as early as in group 2 participants . for pcg , during stmq ( group 1 : left t = 5.09 , right t = 4.64 ; group 2 : left t = 8.71 , right t = 9.24 ; group 3 : left t = 8.79 , right t = 6.66 ; group 4 : left t = 7.83 , right t = 5.68 ) however , in stmn ( group 1 : left t = 4.47 , right t = 5.24 ; group 2 : left t = 10.06 , right t = 9.83 ; group 3 : left t = 7.38 , right t = 6.66 ; group 4 : left t = 5.01 , right t = 4.84 ) , the changes begin to show up in group 4 . for hg , changes of brain laterality both in stmq ( group 1 : left t = 5.58 , right t = 0 ; group 2 : left t = 6.08 , right t = 6.92 ; group 3 : left t = 6.55 , right t = 5.57 ; group 4 : left t = 4.61 , right t = 6.69 ) and stmn ( group 1 ; left t = 5.72 , right t = 0 , group 2 : left t = 5.86 , right t = 6.73 ; group 3 : left t = 8.96 , right t = 6.16 ; group 4 : left t = 0 , right t = 5.44 ) also are shown in group 4 . the demographic and performance accuracy obtained from four groups of participants on the forward repeat task ( frt ) ( in quiet and in 5  db snr ) is shown in table 1 . results indicate that there is no significant difference across groups on performance accuracy on any task . we suggest that aging has minimal effects on both frt ( in quiet and in 5  db snr conditions ) tasks . both tasks comprise passive phonological loop and short - term memory ( stm ) processing in which participants need to memorise a series of words in a short period of time and repeat them forward . our behavioural result is consistent with dobbs and rule , indicating that stm is relatively stable compared to other types of memory processing , and remaining relatively stable until about the age of 70 , at which point it begins to drop . furthermore , our behavioural study is supported by the results which indicate that the human brain has a tremendous capacity to repair itself ; no matter how old the individual is , the brain can modify its structure and function to compensate for the age - related cognitive decline . paired t - tests were conducted to examine if the mean frt in quiet and in noise differed in the four groups of participants . results revealed that the effect of noise on frt was only significant for group 4 . participants in other groups show no significant differences between performance in quiet and in background noise . this may suggest that the deficit of performance in the presence of background noise in group 4 might be related to older adults having difficulties in paying attention to relevant information and ignoring irrelevant information in the environment due to aging [ 39 , 40 ] . the present result is congruent with the fact that aging is associated with difficulty in discriminating speech sounds in noisy environments due to attention deficits [ 21 , 41 ] . we further suggest that this problem also might be linked with degradation of cognitive processing due to aging . therefore , we propose that the impairment in performance in group 4 participants in the noise condition might be linked with deficits in attention in which they are less able to discriminate between background noise and the target stimulus . fmri results reveal that brain behaves differently with different age groups ( tables 2 and 3 ) . results from the laterality index calculation revealed changes in spatial distribution of brain activation patterns , with a leftward asymmetry in the younger groups ( figures 2(a ) and 2(b ) ) , which appears to shift to more rightward asymmetry in the older groups as in figures 3(a ) and 3(b ) . however , the behavioural performances ( as in table 1 ) show no significant differences across the four groups of participants . in the present study , we propose two possibilities to account for changes in hemispheric laterality without changes in task performance . first , we suggest that the aging brain uses different brain circuitry in order to accomplish the same tasks and recruits contralateral brain areas in order to compensate for neural degradation . as people age , they continue to generate new nerve cells and also use more parts of the brain than do young adults . thus , the reorganization of the brain throughout an individual 's life essentially compensates somewhat for neural deficits . other possibility is that cognitive functions in younger adults are more intact compared to those of older adults . thus , the demand is high in older adults in responding to the same cognitive task or stimulus . hence , overrecruitment appears in the right hemisphere of the brain due to the high processing demand and in response to altered function in other brain regions . these could be linked with neural areas in the right hemisphere declining faster than in the left hemisphere , consistent with the differences in grey and white matter ratios in the two hemispheres . the n condition imposed the fewest processing demands , as the participants only needed to listen to the babble noise presented binaurally . activation on stg and mtg was expected given the use of nonverbal auditory stimuli , and results are similar to those observed in normal hearing listeners on tasks using nonverbal stimuli which also demonstrate involvement of the stg . results indicate that all groups of participants activate the same areas of the brain ( table 2 ) . however , results on the laterality index calculation show that there are differences in the shifts of brain laterality with leftward asymmetries in group 1 and group 2 , and more rightward asymmetries in group 3 and group 4 for both the stg and mtg . these age - related differences in the pattern of neural activity suggest that the brain reorganises functional processing by recruiting additional contralateral areas in the brain , something akin to a compensation mechanism . this is supported by the fact that the same general brain regions are used to complete the task . furthermore , there is evidence that when one network of neurons dies , the brain can sprout new connections , creating another network . thus , the increase of neural activity in the right hemisphere in groups 3 and 4 is consistent with the notion of a compensation strategy to ameliorate effects of neural decline . as in tables 3 and 4 , activation of the stg and hg in both stmq and stmn was expected given that auditory stimuli were used and these areas have been associated with auditory processing [ 45 , 46 ] . as we asked our participants to remember the words presented , and at the same time hold the information in memory for subsequent reporting , pcg and post - cg were also activated . these areas are often reported in verbal stm and play important roles in rehearsal of verbal information . moreover , the need to attend might also account for activation of the cerebellum . traditionally , the cerebellum has been thought to be responsible for motor coordination and balance but recently this area is hypothesized to be involved in attention during cognitive tasks [ 48 , 49 ] . the brain is a dynamic and adaptable system ; thus , it might modify its structure and networks in order to compensate for cognitive decline . notably , in comparing effects across the four groups of different ages stmq and stmn , results reveal that there is no specific pattern of a gradual increase or decrease of neural activity in particular regions with age . rather , results are consistent with a reorganization of neural patterns characterized by a shift in hemispheric laterality in the stg , cerebellum , hg , and pcg . results also reveal that these laterality shifts vary from one region to another . finally , noise also influences the laterality changes . in stmq , results indicate that the stg began to shift from leftward to rightward laterality at around the age of participants in group 4 ( 5065 years ) . however , for the stg in stmn , the laterality shift started earlier in age ( group 3 : 4049 years ) . we suggest that the earlier shift in laterality of stg in the 5  db snr could be related to increasing demands of cognitive processing in the aging brain . furthermore , with aging , individuals experience a decreased ability in discriminating speech , even when they have normal hearing acuity . this difficulty is more obvious when the speech is presented in the presence of competing signals ( background noise ) . we propose that this problem might be related to an inability to discriminate between noise and target stimuli , which is a normal aging phenomenon . in hg , we suggest that , during the task , the demand on this area is equally utilized in both conditions and that noisy backgrounds do not influence this processing area . this implies that age - related cognitive decline affects hg in both hemispheres equally , at least in the present task . the cerebellum in both conditions , stmq and stmn , begins to show a shift in hemisphere laterality in people as young as 3039 years ( group 2 participants ) . it is reasonable to suggest that this early shift is related to the cerebellum being more sensitive to aging effects compared to other activated brain areas . this also might suggest that attention plays a major role in the present task , which is to hold the information and suppress irrelevant information and concentrate on the task particularly in the present of background noise . older adults are more distracted by novel irrelevant sounds than younger adults , indicating a relatively larger temporary capture on their attentional resources . deficits in attention and declines in the cognitive system have been shown to be related to anatomical atrophy   and it is also likely that attentional abilities are affected during aging . this is in line with a previous study reporting that older adults with declining sensory perception also have compromised attention . it has also been suggested that the ability to comprehend a cognitive task in challenging situations ( in noisy backgrounds ) is influenced by both auditory and cognitive capacities . age - related changes of brain laterality in older groups are suggested to be a cognitive strategy to ameliorate some of the effects of aging . on the other hand , this adaptive strategy is to maintain performance in the face of decline in the function of canonical neural circuits and may therefore represent evidence of compensation . a related possibility is that additional brain areas in the contralateral hemisphere are recruited because older adults encounter more difficulty and expend more effort on tasks compared to younger adults . in our view , the present findings provide rather convincing support for the idea that changes in brain laterality can be compensatory in the elderly . we further suggest that older brains do things differently , even when behavioural performance is comparable to that of younger adults . collectively , age - related changes in brain structure and function may contribute to poor sensory and cognitive function [ 6 , 54 ] . previous studies found age - related alterations in the anterior - posterior scalp distribution , suggesting a possible decrease in efficiency of attentional processes or that aging alters auditory processing associated with attentional regulation [ 55 , 56 ] . we suggest that aging - related cognitive deficits can be explained by the deficit in attentional abilities . it has been shown that noisy backgrounds capture the attention of the aged more easily than that of the young . finally , these results imply that the aging brain might initiate changes in neural mechanisms which lead to a global reorganization of task - specific neurocognitive networks in order to compensate for decline due to the aging process . we also propose that age - related changes in brain regions including the stg , hg , and cerebellum are task dependent and are influenced by effects of aging . the present study examined and compared age - related neural correlates in four age groups of participants on an auditory stm task performed in quiet and in ( 5  db snr ) multitalker babble noise , in the entire brain using fmri . although all groups of participants activated the same neural areas in processing the stm task , the groups differed in the way such processing took place . such processes reveal differential multiple patterns of brain activity across groups , with a shift from a leftward laterality to a more rightward laterality with aging . changes in hemispheric laterality varied across the different brain regions , with the stg and hg showing late shifting , and the cerebellum showing earlier shifting , with respect to the age of the participants comprising each group . this strongly suggests that the laterality shifts in brain regions vary depending on the sensitivity of the regions to demands of the present tasks . furthermore , results support the hypothesis that the functional networks that underlie attention and auditory processing undergo reorganization during aging and these processes are task dependent . these findings provide novel insights into the patterns of neural compensation in the aging brain .
evidence suggests that cognitive performance deteriorates in noisy backgrounds and the problems are more pronounced in older people due to brain deficits and changes . 
 the present study used functional mri ( fmri ) to investigate the neural correlates of this phenomenon during short - term memory using a forward repeat task performed in quiet ( stmq ) and in noise : 5-db snr ( stmn ) on four groups of participants of different ages . 
 the performance of short - term memory tasks was measured behaviourally . 
 no significant difference was found across age groups in stmq . 
 however , older adults ( 5065 year olds ) performed relatively poorly on the stmn . 
 fmri results on the laterality index indicate changes in hemispheric laterality in the superior temporal gyrus ( stg ) , heschl 's gyrus ( hg ) , and cerebellum , and a leftward asymmetry in younger participants which changes to a more rightward asymmetry in older participants . 
 the results also indicate that the onset of the laterality shift varies from one brain region to another . 
 stg and hg show a late shift while the cerebellum shows an earlier shift . 
 the results also reveal that noise influences this shifting . 
 finally , the results support the hypothesis that functional networks that underlie stg , hg , and cerebellum undergo reorganization to compensate for the neural deficit / cognitive decline .