Age differences in the neural correlates of recollection: transient versus sustained fMRI effects

Prior functional magnetic resonance imaging findings in young adults indicate that recollection-sensitive neural regions dissociate according to the time courses of their respective recollection effects. Here, we examined whether such dissociations are also evident in older adults. Young and older participants encoded a series of word-image pairs, judging which of the denoted objects was the smaller. At the test, participants judged whether each of a series of test words was old or new. If a word was old, the requirement was to recall the associated image and maintain it over a variable delay period. Older adults demonstrated significantly lower associative memory performance than young adults. Transient recollection effects were identified in the left hippocampus, medial prefrontal cortex, and posterior cingulate, while sustained effects were widespread across left lateral cortex and were also evident in the bilateral striatum. Except for those in the left insula, all effects were age-invariant. These findings suggest that both transient and sustained recollection effects are largely stable across much of the healthy adult life span.

Relationships between age, fMRI correlates of familiarity and familiarity-based memory performance under single and dual task conditions

Using fMRI, we investigated the effects of age and divided attention on the neural correlates of familiarity and their relationship with memory performance. At study, word pairs were visually presented to young and older participants under the requirement to make a relational judgment on each pair. Participants were then scanned while undertaking an associative recognition test under single and dual (auditory tone detection) task conditions. The test items comprised studied, rearranged (words from different studied pairs) and new word pairs. fMRI familiarity effects were operationalized as greater activity elicited by studied pairs incorrectly identified as 'rearranged' than by correctly rejected new pairs. The reverse contrast was employed to identify 'novelty' effects. Behavioral familiarity estimates were equivalent across age groups and task conditions. Robust fMRI familiarity effects were identified in several regions, including medial and superior lateral parietal cortex, dorsal medial and left lateral prefrontal cortex, and bilateral caudate. fMRI novelty effects were identified in the anterior medial temporal lobe. Both familiarity and novelty effects were largely age-invariant and did not vary, or varied minimally, according to task condition. In addition, the familiarity effects correlated positively with a behavioral estimate of familiarity strength irrespective of age. These findings extend a previous report from our laboratory, and converge with prior behavioral reports, in demonstrating that the factors of age and divided attention have little impact on behavioral and neural estimates of familiarity.

Relationships between age, fMRI correlates of familiarity and familiarity-based memory performance under single and dual task conditions

Using fMRI, we investigated the effects of age and divided attention on the neural correlates of familiarity and their relationship with memory performance. At study, word pairs were visually presented to young and older participants under the requirement to make a relational judgment on each pair. Participants were then scanned while undertaking an associative recognition test under single and dual (auditory tone detection) task conditions. The test items comprised studied, rearranged (words from different studied pairs) and new word pairs. fMRI familiarity effects were operationalized as greater activity elicited by studied pairs incorrectly identified as 'rearranged' than by correctly rejected new pairs. The reverse contrast was employed to identify 'novelty' effects. Behavioral familiarity estimates were equivalent across age groups and task conditions. Robust fMRI familiarity effects were identified in several regions, including medial and superior lateral parietal cortex, dorsal medial and left lateral prefrontal cortex, and bilateral caudate. fMRI novelty effects were identified in the anterior medial temporal lobe. Both familiarity and novelty effects were age-invariant and did not vary according to task condition. In addition, the familiarity effects correlated positively with a behavioral estimate of familiarity strength irrespective of age. These findings extend a previous report from our laboratory, and converge with prior behavioral reports, in demonstrating that the factors of age and divided attention have minimal impact on behavioral and neural estimates of familiarity.

Cortical thickness, gray matter volume, and cognitive performance: a crosssectional study of the moderating effects of age on their interrelationships

In a sample comprising younger, middle-aged, and older cognitively healthy adults (N = 375), we examined associations between mean cortical thickness, gray matter volume (GMV), and performance in 4 cognitive domains-memory, speed, fluency, and crystallized intelligence. In almost all cases, the associations were moderated significantly by age, with the strongest associations in the older age group. An exception to this pattern was identified in a younger adult subgroup aged <23 years when a negative association between cognitive performance and cortical thickness was identified. Other than for speed, all associations between structural metrics and performance in specific cognitive domains were fully mediated by mean cognitive ability. Cortical thickness and GMV explained unique fractions of the variance in mean cognitive ability, speed, and fluency. In no case, however, did the amount of variance jointly explained by the 2 metrics exceed 7% of the total variance. These findings suggest that cortical thickness and GMV are distinct correlates of domain-general cognitive ability, that the strength and, for cortical thickness, the direction of these associations are moderated by age, and that these structural metrics offer only limited insights into the determinants of individual differences in cognitive performance across the adult lifespan.

The effects of age on neural correlates of recollection: transient versus sustained fMRI effects

Prior fMRI findings in young adults indicate that recollection-sensitive neural regions dissociate according to the time courses of their respective recollection effects. Here, we examined whether such dissociations are also evident in older adults. Young and older participants encoded a series of word-object image pairs, judging which of the denoted objects was the smaller. At test, participants first judged whether a test word was old or new. For items judged old, they were required to recall the associated image and hold it in mind across a variable delay period. A post-delay cue denoted which of three judgments should be made on the retrieved image. Older adults demonstrated significantly lower associative memory performance than young adults. Replicating prior findings, transient recollection effects were identified in the left hippocampus, medial prefrontal cortex and posterior cingulate, while sustained effects were widespread across left lateral cortex and were also evident in the bilateral striatum. With the exception of those in the left insula, all effects were age-invariant. These findings add to the evidence that recollection-related BOLD effects in different neural regions can be temporally dissociated. Additionally, the findings suggest that both transient and sustained recollection effects are largely stable across much of the healthy adult lifespan.

Patterns of retrieval-related cortico-striatal connectivity are stable across the adult lifespan

Memory retrieval effects in the striatum are well documented and robust across experimental paradigms. However, the functional significance of these effects, and whether they are moderated by age, remains unclear. We used functional magnetic resonance imaging paired with an associative recognition task to examine retrieval effects in the striatum in a sample of healthy young, middle-aged, and older adults. We identified anatomically segregated patterns of enhanced striatal blood oxygen level-dependent (BOLD) activity during recollection- and familiarity-based memory judgments. Successful recollection was associated with enhanced BOLD activity in bilateral putamen and nucleus accumbens, and neither of these effects were reliably moderated by age. Familiarity effects were evident in the head of the caudate nucleus bilaterally, and these effects were attenuated in middle-aged and older adults. Using psychophysiological interaction analyses, we observed a monitoring-related increase in functional connectivity between the caudate and regions of the frontoparietal control network, and between the putamen and bilateral retrosplenial cortex and intraparietal sulcus. In all instances, monitoring-related increases in cortico-striatal connectivity were unmoderated by age. These results suggest that the striatum, and the caudate in particular, couples with the frontoparietal control network to support top-down retrieval-monitoring operations, and that the strength of these inter-regional interactions is preserved in later life.

Divided attention at retrieval does not influence neural correlates of recollection in young or older adults

Age-related decline in episodic memory has been partially attributed to older adults' reduced domain general processing resources. In the present study, we examined the effects of divided attention (DA) - a manipulation assumed to further deplete the already limited processing resources of older adults - on the neural correlates of recollection in young and older adults. Participants underwent fMRI scanning while they performed an associative recognition test in single and dual (tone detection) task conditions. Recollection effects were operationalized as greater BOLD activity elicited by test pairs correctly endorsed as 'intact' than pairs correctly or incorrectly endorsed as 'rearranged'. Detrimental effects of DA on associative recognition performance were identified in older but not young adults. The magnitudes of recollection effects did not differ between the single and dual (tone detection) tasks in either age group. Across the task conditions, age-invariant recollection effects were evident in most members of the core recollection network. However, while young adults demonstrated robust recollection effects in left angular gyrus, angular gyrus effects were undetectable in the older adults in either task condition. With the possible exception of this result, the findings suggest that DA did not influence processes supporting the retrieval and representation of associative information in either young or older adults, and converge with prior behavioral findings to suggest that episodic retrieval operations are little affected by DA.

Specific and general relationships between cortical thickness and cognition in older adults: a longitudinal study

Prior studies suggest that relationships between regional cortical thickness and domain-specific cognitive performance can be mediated by the relationship between global cortical thickness and domain-general cognition. Whether such findings extend to longitudinal cognitive change remains unclear. Here, we examined the relationships in healthy older adults between cognitive performance, longitudinal cognitive change over 3 years, and cortical thickness at baseline of the left and right inferior frontal gyrus (IFG) and left and right hemispheres. Both right IFG and right hemisphere thickness predicted baseline general cognition and domain-specific cognitive performance. Right IFG thickness was also predictive of longitudinal memory change. However, right IFG thickness was uncorrelated with cognitive performance and memory change after controlling for the mean thickness of other ipsilateral cortical regions. In addition, most identified associations between cortical thickness and specific cognitive domains were nonsignificant after controlling for the variance shared with other cognitive domains. Thus, relationships between right IFG thickness, cognitive performance, and memory change appear to be largely accounted for by more generic relationships between cortical thickness and cognition. This article is part of the Virtual Special Issue titled "COGNITIVE NEUROSCIENCE OF HEALTHY AND PATHOLOGICAL AGING". The full issue can be found on ScienceDirect athttps://www.sciencedirect.com/journal/neurobiology-of-aging/special-issue/105379XPWJP.

Neural correlates of post-retrieval monitoring in older adults are preserved under divided attention, but are decoupled from memory performance

Post-retrieval monitoring is associated with engagement of anterior cingulate and dorsolateral prefrontal cortex. Recent fMRI studies reported age-invariant monitoring effects in these regions and an age-invariant correlation between these effects and memory performance. The present study examined monitoring effects during associative recognition (difference in activity elicited by 'rearranged' and 'intact' test pairs) under single and dual (tone detection) task conditions in young and older adults (Ns = 28 per group). It was predicted that, for the older adults only, dual tasking would attenuate memory performance and monitoring effects and weaken their correlation. Consistent with this prediction, in the older group imposition of the secondary task led to lower memory performance and elimination of the relationship between monitoring effects and performance. However, the size of the effects did not differ between single and dual task conditions. The findings suggest that the decline in older adults' memory performance in the dual task condition resulted not from impaired monitoring, but from a different cause that also weakened the dependence of performance on monitoring.

Recollection-related hippocampal fMRI effects predict longitudinal memory change in healthy older adults

Prior fMRI studies have reported relationships between memory-related activity in the hippocampus and in-scanner memory performance, but whether such activity is predictive of longitudinal memory change remains unclear. Here, we administered a neuropsychological test battery to a sample of cognitively healthy older adults on three occasions, the second and third sessions occurring one month and three years after the first session. Structural and functional MRI data were acquired between the first two sessions. The fMRI data were derived from an associative recognition procedure and allowed estimation of hippocampal effects associated with both successful associative encoding and successful associative recognition (recollection). Baseline memory performance and memory change were evaluated using memory component scores derived from a principal components analysis of the neuropsychological test scores. Across participants, right hippocampal encoding effects correlated significantly with baseline memory performance after controlling for chronological age. Additionally, both left and right hippocampal associative recognition effects correlated negatively with longitudinal memory decline after controlling for age, and the relationship with the left hippocampal effect remained after also controlling for left hippocampal volume. Thus, in cognitively healthy older adults, the magnitude of hippocampal recollection effects appears to be a robust predictor of future memory change.

Recollection-related increases in functional connectivity across the healthy adult lifespan

In young adults, recollection-sensitive brain regions exhibit enhanced connectivity with a widely distributed set of other regions during successful versus unsuccessful recollection, and the magnitude of connectivity change correlates with individual differences in recollection accuracy. Here, we examined whether recollection-related changes in connectivity and their relationship with performance varied across samples of young, middle-aged, and older adults. Psychophysiological interaction analyses identified recollection-related increases in connectivity both with recollection-sensitive seed regions and among regions distributed throughout the whole brain. The seed-based approach failed to identify age-related differences in recollection-related connectivity change. However, the whole-brain analysis revealed a number of age-related effects. Numerous pairs of regions exhibited a main effect of age on connectivity change, mostly due to decreased change with increasing age. After controlling for recollection accuracy, however, these effects of age were for the most part no longer significant, and those effects that were detected now reflected age-related increases in connectivity change. A subset of pairs of regions also exhibited an age by performance interaction, driven mostly by a weaker relationship between connectivity change and recollection accuracy with increasing age. We conjecture that these effects reflect age-related differences in neuromodulation.

Independent contributions of fMRI familiarity and novelty effects to recognition memory and their stability across the adult lifespan

The impact of age on the neural correlates of familiarity-driven recognition memory has received relatively little attention. Here, the relationships between age, the neural correlates of familiarity, and memory performance were investigated using an associative recognition test in young, middle-aged and older participants. Test items comprised studied, rearranged (items studied on different trials) and new word pairs. fMRI 'familiarity effects' were operationalized as greater activity for studied test pairs incorrectly identified as 'rearranged' than for correctly rejected new pairs. The reverse contrast was employed to identify 'novelty' effects. Estimates of familiarity strength were slightly but significantly lower for the older relative to the younger group. With the exception of one region in dorsal medial prefrontal cortex, fMRI familiarity effects (which were identified in medial and lateral parietal cortex, dorsal medial and left lateral prefrontal cortex, and bilateral caudate among other regions) did not differ significantly with age. Age-invariant 'novelty effects' were identified in the anterior hippocampus and the perirhinal cortex. When entered into the same regression model, familiarity and novelty effects independently predicted familiarity strength across participants, suggesting that the two classes of memory effect reflect functionally distinct mnemonic processes. It is concluded that the neural correlates of familiarity-based memory judgments, and their relationship with familiarity strength, are largely stable across much of the healthy adult lifespan.

The relationships between age, associative memory performance, and the neural correlates of successful associative memory encoding

Using functional magnetic resonance imaging, subsequent memory effects (greater activity for later remembered than later forgotten study items) predictive of associative encoding were compared across samples of young, middle-aged, and older adults (total N = 136). During scanning, participants studied visually presented word pairs. In a later test phase, they discriminated between studied pairs, "rearranged" pairs (items studied on different trials), and new pairs. Subsequent memory effects were identified by contrasting activity elicited by study pairs that went on to be correctly judged intact or incorrectly judged rearranged. Effects in the hippocampus were age-invariant and positively correlated across participants with associative memory performance. Subsequent memory effects in the right inferior frontal gyrus (IFG) were greater in the older than the young group. In older participants only, both left and, in contrast to prior reports, right IFG subsequent memory effects correlated positively with memory performance. We suggest that the IFG is especially vulnerable to age-related decline in functional integrity and that the relationship between encoding-related activity in right IFG and memory performance depends on the experimental context.

The effects of study task on prestimulus subsequent memory effects in the hippocampus

Functional magnetic resonance imaging (fMRI) was employed to examine the effects of a study task manipulation on pre-stimulus activity in the hippocampus predictive of later successful recollection. Eighteen young participants were scanned while making either animacy or syllable judgments on visually presented study words. Cues presented before each word denoted which judgment should be made. Following the study phase, a surprise recognition memory test was administered in which each test item had to be endorsed as "Remembered," "Known," or "New." As expected, "deep" animacy judgments led to better memory for study items than did "shallow" syllable judgments. In both study tasks, pre-stimulus subsequent recollection effects were evident in the interval between the cue and the study item in bilateral anterior hippocampus. However, the direction of the effects differed according to the study task: whereas pre-stimulus hippocampal activity on animacy trials was greater for later recollected items than items judged old on the basis of familiarity (replicating prior findings), these effects reversed for syllable trials. We propose that the direction of pre-stimulus hippocampal subsequent memory effects depends on whether an optimal pre-stimulus task set facilitates study processing that is conducive or unconducive to the formation of contextually rich episodic memories.

The Effects of Age on the Neural Correlates of Recollection Success, Recollection-Related Cortical Reinstatement, and Post-Retrieval Monitoring

Functional magnetic resonance imaging (fMRI) was used to investigate whether age-related differences in episodic memory performance are accompanied by a reduction in the specificity of recollected information. We addressed this question by comparing recollection-related cortical reinstatement in young and older adults. At study, subjects viewed objects and concrete words, making 1 of 2 different semantic judgments depending on the study material. Test items were words that corresponded to studied words or the names of studied objects. Subjects indicated whether each test item was recollected, familiar, or novel. Reinstatement of information differentiating the encoding tasks was quantified both with a univariate analysis of the fMRI signal and with a multivoxel pattern analysis, using a classifier that had been trained to discriminate between the 2 classes of study episode. The results of these analyses converged to suggest that reinstatement did not differ according to age. Thus, there was no evidence that specificity of recollected information was reduced in older individuals. Additionally, there were no age effects in the magnitude of recollection-related modulations in regional activity or in the neural correlates of post-retrieval monitoring. Taken together, the findings suggest that the neural mechanisms engaged during successful episodic retrieval can remain stable with advancing age.

Pre-stimulus neural activity predicts successful encoding of inter-item associations

fMRI was employed to investigate the relationship between pre-stimulus neural activity and associative encoding of words and pictures in humans. While undergoing scanning, subjects studied randomly interleaved word or picture pairs. A pre-stimulus cue preceded the presentation of each study pair and signaled whether it would comprise words or pictures. Memory for the study pairs was later tested with an associative recognition test, which comprised word or picture pairs presented either in the same (intact) or a different (rearranged) pairing as at study, along with pairs of new items. The critical fMRI contrast was between study activity associated with pairs later correctly judged intact and pairs incorrectly judged as rearranged. A key question was whether material-selective pre-stimulus encoding effects could be identified which overlapped regions selectively activated by the respective study material. Picture-selective pre-stimulus effects were identified in bilateral fusiform and the intraparietal sulcus (IPS), whereas word-selective effects could not be identified. Material-invariant pre-stimulus subsequent memory effects were also identified in several neocortical regions as well as in the hippocampus. Whereas the loci of the neocortical effects suggest that they reflect the benefit to encoding that accrues from engagement of cognitive control processes, their magnitude was negatively correlated across subjects with associative recognition performance and positively related to false alarm rate. Conversely, the hippocampal effects also predicted unique variance in associative memory and were negatively related to hit rate. It is suggested that the neocortical pre-stimulus effects may reflect encoding processes that increase familiarity of single items, whereas the hippocampal pre-stimulus effects are proposed to reflect either the encoding of task-irrelevant features or the retrieval of task-relevant information associated with the pre-stimulus cues. Overall, the results provide evidence that pre-stimulus processes may be deleterious, rather than beneficial, to associative encoding.

The relationship between task-related and subsequent memory effects

The primary aim of this fMRI study was to assess the proposal that negative subsequent memory effects-greater activity for later forgotten relative to later remembered study items-are localized to regions demonstrating task-negative effects, and hence to potential components of the default mode network. Additionally, we assessed whether positive subsequent memory effects overlapped with regions demonstrating task-positive effects. Eighteen participants were scanned while they made easy or difficult relational judgments on visually presented word pairs. Easy and hard task blocks were interleaved with fixation-only rest periods. In the later unscanned test phase, associative recognition judgments were required on intact word pairs (studied pairs), rearranged pairs (pairs formed from words presented on different study trials) and new pairs. Subsequent memory effects were identified by contrasting the activity elicited by study pairs that went on to be correctly endorsed as intact versus incorrectly endorsed as rearranged. Task effects were identified by contrasting all study items and rest blocks. Both task-negative and task-positive effects were evident in widespread cortical regions and negative and positive subsequent memory effects were generally confined to task-negative and task-positive regions respectively. However, subsequent memory effects could be identified in only a fraction of task-sensitive voxels and, unlike task effects, were insensitive to the difficulty manipulation. The findings for the negative subsequent memory effects are consistent with recent proposals that the default mode network is functionally heterogeneous, and suggest that these effects are not accurately characterized as reflections of the modulation of the network as a whole.

Comparison of the neural correlates of encoding item-item and item-context associations

fMRI was employed to investigate the role of the left inferior frontal gyrus (LIFG) in the encoding of item-item and item-context associations. On each of a series of study trials subjects viewed a picture that was presented either to the left or right of fixation, along with a subsequently presented word that appeared at fixation. Memory was tested in a subsequent memory test that took place outside of the scanner. On each test trial one of two forced choice judgments was required. For the associative test, subjects chose between the word paired with the picture at study and a word studied on a different trial. For the source test, the judgment was whether the picture had been presented on the left or right. Successful encoding of associative information was accompanied by subsequent memory effects in several cortical regions, including much of the LIFG. By contrast, successful source encoding was selectively associated with a subsequent memory effect in right fusiform cortex. The finding that the LIFG was enhanced during successful associative, but not source, encoding is interpreted in light of the proposal that subsequent memory effects are localized to cortical regions engaged by the on-line demands of the study task.

Effects of age on negative subsequent memory effects associated with the encoding of item and item-context information

It has consistently been reported that "negative" subsequent memory effects--lower study activity for later remembered than later forgotten items--are attenuated in older individuals. The present functional magnetic resonance imaging study investigated whether these findings extend to subsequent memory effects associated with successful encoding of item-context information. Older (n = 25) and young (n = 17) subjects were scanned while making 1 of 2 encoding judgments on a series of pictures. Memory was assessed for the study item and, for items judged old, the item's encoding task. Both memory judgments were made using confidence ratings, permitting item and source memory strength to be unconfounded and source confidence to be equated across age groups. Replicating prior findings, negative item effects in regions of the default mode network in young subjects were reversed in older subjects. Negative source effects, however, were invariant with respect to age and, in both age groups, the magnitude of the effects correlated with source memory performance. It is concluded that negative item effects do not reflect processes necessary for the successful encoding of item-context associations in older subjects. Negative source effects, in contrast, appear to reflect the engagement of processes that are equally important for successful episodic encoding in older and younger individuals.

Neural correlates of the encoding of multimodal contextual features

Functional magnetic resonance imaging (fMRI) was employed to identify neural regions engaged during the encoding of contextual features belonging to different modalities. Subjects studied objects that were presented to the left or right of fixation. Each object was paired with its name, spoken in either a male or a female voice. The test requirement was to discriminate studied from unstudied pictures and, for each picture judged old, to retrieve its study location and the gender of the voice that spoke its name. Study trials associated with accurate rather than inaccurate location memory demonstrated enhanced activity in the fusiform and parahippocampal cortex and the hippocampus and reduced activity (a negative subsequent memory effect) in the medial occipital cortex. Successful encoding of voice information was associated with enhanced study activity in the right middle superior temporal sulcus and activity reduction in the right superior frontal cortex. These findings support the proposal that encoding of a contextual feature is associated with enhanced activity in regions engaged during its online processing. In addition, they indicate that negative subsequent memory effects can also demonstrate feature-selectivity. Relative to other classes of study trials, trials for which both contextual features were later retrieved demonstrated enhanced activity in the lateral occipital complex and reduced activity in the temporo-parietal junction. These findings suggest that multifeatural encoding was facilitated when the study item was processed efficiently and study processing was not interrupted by redirection of attention toward extraneous events.

Effects of age on the neural correlates of familiarity as indexed by ERPs

ERPs were recorded from samples of young (18-29 years) and older (63-77 years) participants while they performed a modified "remember-know" recognition memory test. ERP correlates of familiarity-driven recognition were obtained by contrasting the waveforms elicited by unrecollected test items accorded "confident old" and "confident new" judgments. Correlates of recollection were identified by contrasting the ERPs elicited by items accorded "remember" and confident old judgments. Behavioral analyses revealed lower estimates of both recollection and familiarity in older participants than in young participants. The putative ERP correlate of recollection-the "left parietal old-new effect"-was evident in both age groups, although it was slightly but significantly smaller in the older sample. By contrast, the putative ERP correlate of familiarity-the "midfrontal old-new effect"-could be identified in young participants only. This age-related difference in the sensitivity of ERPs to familiarity was also evident in subgroups of young and older participants, in whom familiarity-based recognition performance was equivalent. Thus, the inability to detect a reliable midfrontal old-new effect in older participants was not a consequence of an age-related decline in the strength of familiarity. These findings raise the possibility that familiarity-based recognition memory depends upon qualitatively different memory signals in older and young adults.

The effects of age, memory performance, and callosal integrity on the neural correlates of successful associative encoding

This functional magnetic resonance imaging study investigated the relationship between the neural correlates of associative memory encoding, callosal integrity, and memory performance in older adults. Thirty-six older and 18 young subjects were scanned while making relational judgments on word pairs. Neural correlates of successful encoding (subsequent memory effects) were identified by contrasting the activity elicited by study pairs that were correctly identified as having been studied together with the activity elicited by pairs wrongly judged to have come from different study trials. Subsequent memory effects common to the 2 age groups were identified in several regions, including left inferior frontal gyrus and bilateral hippocampus. Negative effects (greater activity for forgotten than for remembered items) in default network regions in young subjects were reversed in the older group, and the amount of reversal correlated negatively with memory performance. Additionally, older subjects' subsequent memory effects in right frontal cortex correlated positively with anterior callosal integrity and negatively with memory performance. It is suggested that recruitment of right frontal cortex during verbal memory encoding may reflect the engagement of processes that compensate only partially for age-related neural degradation.

Changes in familiarity and recollection across the lifespan: an ERP perspective

The ability to recognize previous experience depends on two neurocognitive processes, familiarity, fast-acting and relatively automatic, and recollection, slower-acting and more effortful. Familiarity appears to mature relatively early in development and is maintained with aging, whereas recollection shows protracted development and deteriorates with aging. To assess this model, ERP and behavioral data were recorded in children (9-10 years), adolescents (13-14), young (20-30) and older (65-85) adults during a recognition memory task in which the same items were studied and tested over four cycles. Participants decided whether each item was old or new and then whether the decision was associated with (Remember, R) or without (Know, K) contextual detail. Memory sensitivity was greatest in young adults, although all groups showed increases in memory sensitivity and R judgments with repetition. Familiarity-based processes (mid-frontal episodic memory, EM, effect) appeared to be used by adolescents, young and older adults, but apparently not to the same extent by children. Recollection-based processes (parietal EM effect) were recruited by children, adolescents and young adults, but to a much lesser extent by older adults. Repetition enhanced the parietal effect in all but older adults. However, post-hoc analyses indicated that reduced recollective processing was confined to poor-performing older adults. By contrast, children appeared to rely mainly on recollection concordant with their conservative decision criteria across tests. We conclude that episodic-memory development reflects the increasingly flexible and interchangeable use of familiarity and recollection with a breakdown in the latter at older ages, perhaps limited to poor-performing older adults.

The development of control processes supporting source memory discrimination as revealed by event-related potentials

Improvement in source memory performance throughout childhood is thought to be mediated by the development of executive control. As postretrieval control processes may be better time-locked to the recognition response rather than the retrieval cue, the development of processes underlying source memory was investigated with both stimulus- and response-locked event-related potentials (ERPs). These were recorded in children, adolescents, and adults during a recognition memory exclusion task. Green- and red-outlined pictures were studied, but were tested in black outline. The test requirement was to endorse old items shown in one study color ("targets") and to reject new items along with old items shown in the alternative study color ("nontargets"). Source memory improved with age. All age groups retrieved target and nontarget memories as reflected by reliable parietal episodic memory (EM) effects, a stimulus-locked ERP correlate of recollection. Response-locked ERPs to targets and nontargets diverged in all groups prior to the response, although this occurred at an increasingly earlier time point with age. We suggest these findings reflect the implementation of attentional control mechanisms to enhance target memories and facilitate response selection with the greatest and least success, respectively, in adults and children. In adults only, response-locked ERPs revealed an early-onsetting parietal negativity for nontargets, but not for targets. This was suggested to reflect adults' ability to consistently inhibit prepotent target responses for nontargets. The findings support the notion that the development of source memory relies on the maturation of control processes that serve to enhance accurate selection of task-relevant memories.

On the elusive nature of sex differences in cognition: hormonal influences contributing to within-sex variation

We argue that within-sex variation resulting from the prenatal organizational and adult activational effects of gonadal steroid hormones has the potential to obscure between sex differences in cognitive performance and functional cerebral asymmetry. Two putative markers for prenatal testosterone, finger ridge count (FRC) asymmetry and the 2D:4D finger length ratio, have been linked to within-sex variation in cognitive performance. In particular, FRC allows the identification of men and women who show a reversal of the typical sex-related pattern of task performance. Three paradigms for the study of activational effects--seasonal, menstrual, and diurnal hormonal cycles--have evaluated changes in task performance and functional cerebral asymmetry. The performance of sex-dimorphic, but not sex-neutral, tasks changes with estrogen across the menstrual cycle and with testosterone across its seasonal and diurnal cycles. Functional cerebral asymmetry also changes systematically across both the menstrual cycle and the diurnal testosterone cycle in such a way that suggests left hemisphere performance increases as testosterone levels decline whereas right hemisphere performance increases as estrogen levels decline. In studies of sex differences, such correlates of within-sex hormone-related differences are rarely measured or controlled. Whatever the explanation for the associations of putative markers and hormone cycles with differences in cognitive abilities and cerebral asymmetry, it is clear that these relationships have the potential to contribute to the elusive nature of sex differences in cognition and functional brain organization.