An evaluation of distinct volumetric and functional MRI contributions toward understanding age and task performance: a study in the basal ganglia

Age differences in sustained attention tasks: A meta-analysis

Many aspects of attention decline with aging. There is a current debate on how aging also affects sustained attention. In this study, we contribute to this debate by meta-analytically comparing performance on the go/no-go Sustained Attention to Response Task (SART) in younger and older adults. We included only studies in which the SART had a low proportion of no-go trials (5%–30%), there was a random or quasirandom stimulus presentation, and data on both healthy younger and older adults were available. A total of 12 studies were suitable with 832 younger adults and 690 older adults. Results showed that older adults were slower than younger adults on go trials (g = 1, 95% CI [.72, 1.27]) and more accurate than younger adults on no-go trials (g = .59, 95% CI [.32, .85]). Moreover, older adults were slower after a no-go error than younger adults (g = .79, 95% CI [.60, .99]). These results are compatible with an age-related processing speed deficit, mostly suggested by longer go RTs, but also with an increased preference for a prudent strategy, as demonstrated by fewer no-go errors and greater posterror slowing in older adults. An inhibitory deficit account could not explain these findings, as older adults actually outperformed younger adults by producing fewer false alarms to no-go stimuli. These findings point to a more prudent strategy when using attentional resources in aging that allows reducing the false-alarm rate in tasks producing a tendency for automatic responding.

A Lifespan Model of Interference Resolution and Inhibitory Control: Risk for Depression and Changes with Illness Progression

The cognitive processes involved in inhibitory control accuracy (IC) and interference resolution speed (IR) or broadly - inhibition - are discussed in this review, and both are described within the context of a lifespan model of mood disorders. Inhibitory control (IC) is a binary outcome (success or no for response selection and inhibition of unwanted responses) for any given event that is influenced to an extent by IR. IR refers to the process of inhibition, which can be manipulated by task design in earlier and later stages through use of distractors and timing, and manipulation of individual differences in response proclivity. We describe the development of these two processes across the lifespan, noting factors that influence this development (e.g., environment, adversity and stress) as well as inherent difficulties in assessing IC/IR prior to adulthood (e.g., cross-informant reports). We use mood disorders as an illustrative example of how this multidimensional construct can be informative to state, trait, vulnerability and neuroprogression of disease. We present aggregated data across numerous studies and methodologies to examine the lifelong development and degradation of this subconstruct of executive function, particularly in mood disorders. We highlight the challenges in identifying and measuring IC/IR in late life, including specificity to complex, comorbid disease processes. Finally, we discuss some potential avenues for treatment and accommodation of these difficulties across the lifespan, including newer treatments using cognitive remediation training and neuromodulation.

Diffusion Kurtosis Imaging of Microstructural Changes in Gray Matter Nucleus in Parkinson Disease

Objective: To explore the microstructural damage of extrapyramidal system gray matter nuclei in Parkinson disease (PD) using diffusion kurtosis imaging (DKI). Materials and Methods: We enrolled 35 clinically confirmed PD patients and 23 healthy volunteers. All patients underwent MR examination with conventional MRI scan sequences and an additional DKI sequence. We subsequently reconstructed the DKI raw images and analyzed the data. A radiologist in our hospital collected the Mini-Mental State Examination (MMSE) score of all subjects. Results: In the PD group, the mean kurtosis and axial kurtosis level decreased in the red nucleus (RN) and thalamus; the radial kurtosis increased in the substantia nigra (SN) and globus pallidus (GP). Fractional anisotropy decreased in the putamen. The largest area under the ROC curve of mean diffusion in GP was 0.811. Most kurtosis parameters demonstrated a positive correlation with the MMSE score, while several diffusion parameters showed a negative correlation with the same. Conclusion: DKI can qualitatively distinguish PD from healthy controls; furthermore, DKI-derived parameters can quantitatively evaluate the modifications of microstructures in extrapyramidal system gray matter nucleus in PD.

Cognitive Control as a 5-HT1A-Based Domain That Is Disrupted in Major Depressive Disorder

Heterogeneity within Major Depressive Disorder (MDD) has hampered identification of biological markers (e.g., intermediate phenotypes, IPs) that might increase risk for the disorder or reflect closer links to the genes underlying the disease process. The newer characterizations of dimensions of MDD within Research Domain Criteria (RDoC) domains may align well with the goal of defining IPs. We compare a sample of 25 individuals with MDD compared to 29 age and education matched controls in multimodal assessment. The multimodal RDoC assessment included the primary IP biomarker, positron emission tomography (PET) with a selective radiotracer for 5-HT1A [(11C)WAY-100635], as well as event-related functional MRI with a Go/No-go task targeting the Cognitive Control network, neuropsychological assessment of affective perception, negative memory bias and Cognitive Control domains. There was also an exploratory genetic analysis with the serotonin transporter (5-HTTLPR) and monamine oxidase A (MAO-A) genes. In regression analyses, lower 5-HT1A binding potential (BP) in the MDD group was related to diminished engagement of the Cognitive Control network, slowed resolution of interfering cognitive stimuli, one element of Cognitive Control. In contrast, higher/normative levels of 5-HT1A BP in MDD (only) was related to a substantial memory bias toward negative information, but intact resolution of interfering cognitive stimuli and greater engagement of Cognitive Control circuitry. The serotonin transporter risk allele was associated with lower 1a BP and the corresponding imaging and cognitive IPs in MDD. Lowered 5HT 1a BP was present in half of the MDD group relative to the control group. Lowered 5HT 1a BP may represent a subtype including decreased engagement of Cognitive Control network and impaired resolution of interfering cognitive stimuli. Future investigations might link lowered 1a BP to neurobiological pathways and markers, as well as probing subtype-specific treatment targets.

The double burden of age and major depressive disorder on the cognitive control network

Poor cognitive control (CC) is common among older individuals with major depressive disorder (OMDD). At the same time, studies of CC in OMDD with fMRI are relatively limited and often have small samples. The present study was conducted to further examine poor CC in OMDD with early onset depression, as well as to investigate the interactive effects of MDD and aging on cognitive control. Twenty OMDD, 17 older never-depressed comparisons (ONDC), 16 younger adults with MDD (YMDD), and 18 younger never-depressed comparisons (YNDC) participated. All participants completed the Go level of the Parametric Go/No-Go Test, which requires sustained attention and inhibitory control while undergoing functional MRI (fMRI). YNDC were faster in reaction times (RTs) to go targets relative to the other 3 groups, and the YMDD group was faster than the OMDD group. fMRI effects of both age and diagnosis were present, with greater activation in MDD, and in aging. Additionally, the interaction of age and MDD was also significant, such that OMDD exhibited greater recruitment of fronto-subcortical regions relative to older comparisons. These results are consistent with prior research reporting that OMDD recruit more fronto-striatal regions in order to perform at the same level as their never-depressed peers, here on a task of sustained attention and inhibitory control. There may be an interaction of cognitive aging and depression to create a double burden on the CC network in OMDD, including possible fronto-striatal compensation during CC that is unique to OMDD, as younger MDD individuals do not show this pattern.

Decoupling of the amygdala to other salience network regions in adolescent-onset recurrent major depressive disorder

BACKGROUND

Recent meta-analyses of resting-state networks in major depressive disorder (MDD) implicate network disruptions underlying cognitive and affective features of illness. Heterogeneity of findings to date may stem from the relative lack of data parsing clinical features of MDD such as phase of illness and the burden of multiple episodes.

METHOD

Resting-state functional magnetic resonance imaging data were collected from 17 active MDD and 34 remitted MDD patients, and 26 healthy controls (HCs) across two sites. Participants were medication-free and further subdivided into those with single v. multiple episodes to examine disease burden. Seed-based connectivity using the posterior cingulate cortex (PCC) seed to probe the default mode network as well as the amygdala and subgenual anterior cingulate cortex (sgACC) seeds to probe the salience network (SN) were conducted.

RESULTS

Young adults with remitted MDD demonstrated hyperconnectivity of the left PCC to the left inferior frontal gyrus and of the left sgACC to the right ventromedial prefrontal cortex (PFC) and left hippocampus compared with HCs. Episode-independent effects were observed between the left PCC and the right dorsolateral PFC, as well as between the left amygdala and right insula and caudate, whereas the burden of multiple episodes was associated with hypoconnectivity of the left PCC to multiple cognitive control regions as well as hypoconnectivity of the amygdala to large portions of the SN.

CONCLUSIONS

This is the first study of a homogeneous sample of unmedicated young adults with a history of adolescent-onset MDD illustrating brain-based episodic features of illness.

Response inhibition in the parametric go/no-go task and its relation to impulsivity and subclinical psychopathy

The current study utilizes the parametric go/no-go task (PGNG), a task that examines changes in inhibitory performance as executive function load increases, to examine the link between psychopathic traits, impulsivity, and response inhibition in a cohort of healthy participants. The results show that as executive function load increased, inhibitory ability decreased. High scores on the Cognitive Complexity subscale of the Barratt Impulsivity Scale (BIS-11) predict poor inhibitory ability in the PGNG. Similarly, high scores on the Psychopathy Personality Inventory-Revised (PPI-R) Blame Externalization subscale predict response inhibition deficits in the PGNG, which loads more on the executive functions than the standard go/no-go task. The remaining BIS-11 as well as PPI-R subscales did not interact with inhibitory performance in the PGNG highlighting the specificity of associations between aspects of personality and impulsivity with inhibitory performance as cognitive load is increased. These data point towards the sensitivity of the PGNG in studying response inhibition in the context of highly impulsive populations and its utility as a measure of impulsivity.

Alteration of Brain Functional Networks in Early-Stage Parkinson's Disease: A Resting-State fMRI Study

Although alterations of topological organization have previously been reported in the brain functional network of Parkinson's disease (PD) patients, the topological properties of the brain network in early-stage PD patients who received antiparkinson treatment are largely unknown. This study sought to determine the topological characteristics of the large-scale functional network in early-stage PD patients. First, 26early-stage PD patients (Hoehn and Yahr stage:1-2) and 30 age-matched normal controls were scanned using resting-state functional MRI. Subsequently, graph theoretical analysis was employed to investigate the abnormal topological configuration of the brain network in early-stage PD patients. We found that both the PD patient and control groups showed small-world properties in their functional brain networks. However, compared with the controls, the early-stage PD patients exhibited abnormal global properties, characterized by lower global efficiency. Moreover, the modular structure and the hub distribution were markedly altered in early-stage PD patients. Furthermore, PD patients exhibited increased nodal centrality, primarily in the bilateral pallidum, the inferior parietal lobule, and the medial superior frontal gyrus, and decreased nodal centrality in the caudate nucleus, the supplementary motor areas, the precentral gyrus, and the middle frontal gyrus. There were significant negative correlations between the Unified Parkinson Disease Rating Scale motor scores and nodal centralities of superior parietal gyrus. These results suggest that the topological organization of the brain functional network was altered in early-stage PD patients who received antiparkinson treatment, and we speculated that the antiparkinson treatment may affect the efficiency of the brain network to effectively relieve clinical symptoms of PD.

The significance of caudate volume for age-related associative memory decline

Aging comes along with reduced gray matter (GM) volume in several cerebral areas and with cognitive performance decline in different cognitive domains. Moreover, regional GM volume is linked to specific cognitive sub processes in older adults. However, it remains unclear which regional changes in older individuals are directly associated with decreased cognitive performance. Moreover, most of the studies on this topic focused on hippocampal and prefrontal brain regions and their relation to memory and executive functioning. Interestingly, there are only a few studies that reported an association between striatal brain volume and cognitive performance. This is insofar surprising that striatal structures are (1) highly affected by age and (2) involved in different neural circuits that serve intact cognition. To address these issues, voxel-based morphometry (VBM) was used to analyze GM volume in 18 younger and 18 older adults. Moreover, several neuropsychological tests from different neuropsychological test batteries were applied to assess a broad range of cognitive domains. Older adults showed less GM volume than younger adults within frontal, striatal, and cerebellar brain regions. In the group of older adults, significant correlations were found between striatal GM volume and memory performance and between prefrontal/temporal GM volume and executive functioning. The only direct overlap between brain regions associated with regional atrophy and cognitive performance in older adults was found for the right caudate: older adults showed reduced caudate volume relative to younger adults. Moreover, caudate volume was positively correlated with associative memory accuracy in older adults and older adults showed poorer performances than younger adults in the respective associative memory task. Taken together, the current findings indicate the relevance of the caudate for associative memory decline in the aging brain.

Age-related alterations in the expression of genes and synaptic plasticity associated with nitric oxide signaling in the mouse dorsal striatum

Age-related alterations in the expression of genes and corticostriatal synaptic plasticity were studied in the dorsal striatum of mice of four age groups from young (2-3 months old) to old (18-24 months of age) animals. A significant decrease in transcripts encoding neuronal nitric oxide (NO) synthase and receptors involved in its activation (NR1 subunit of the glutamate NMDA receptor and D1 dopamine receptor) was found in the striatum of old mice using gene array and real-time RT-PCR analysis. The old striatum showed also a significantly higher number of GFAP-expressing astrocytes and an increased expression of astroglial, inflammatory, and oxidative stress markers. Field potential recordings from striatal slices revealed age-related alterations in the magnitude and dynamics of electrically induced long-term depression (LTD) and significant enhancement of electrically induced long-term potentiation in the middle-aged striatum (6-7 and 12-13 months of age). Corticostriatal NO-dependent LTD induced by pharmacological activation of group I metabotropic glutamate receptors underwent significant reduction with aging and could be restored by inhibition of cGMP hydrolysis indicating that its age-related deficit is caused by an altered NO-cGMP signaling cascade. It is suggested that age-related alterations in corticostriatal synaptic plasticity may result from functional alterations in receptor-activated signaling cascades associated with increasing neuroinflammation and a prooxidant state.

The effects of age on resting state functional connectivity of the basal ganglia from young to middle adulthood

The basal ganglia nuclei are critical for a variety of cognitive and motor functions. Much work has shown age-related structural changes of the basal ganglia. Yet less is known about how the functional interactions of these regions with the cerebral cortex and the cerebellum change throughout the lifespan. Here, we took advantage of a convenient sample and examined resting state functional magnetic resonance imaging data from 250 adults 18 to 49 years of age, focusing specifically on the caudate nucleus, pallidum, putamen, and ventral tegmental area/substantia nigra (VTA/SN). There are a few main findings to report. First, with age, caudate head connectivity increased with a large region of ventromedial prefrontal/medial orbitofrontal cortex. Second, across all subjects, pallidum and putamen showed negative connectivity with default mode network (DMN) regions such as the ventromedial prefrontal cortex and posterior cingulate cortex, in support of anti-correlation of the "task-positive" network (TPN) and DMN. This negative connectivity was reduced with age. Furthermore, pallidum, posterior putamen and VTA/SN connectivity to other TPN regions, such as somatomotor cortex, decreased with age. These results highlight a distinct effect of age on cerebral functional connectivity of the dorsal striatum and VTA/SN from young to middle adulthood and may help research investigating the etiologies or monitoring outcomes of neuropsychiatric conditions that implicate dopaminergic dysfunction.

Differential prefrontal and subcortical circuitry engagement during encoding of semantically related words in patients with late-life depression

OBJECTIVE

Verbal memory difficulties are common among individuals with late-life depression (LLD), though there is limited knowledge about disruptions to underlying cerebral circuitry. The purpose of this study is to examine aberrations to cerebral networks implicated in encoding novel verbal semantic material among older adults with LLD.

METHODS

Twenty-four older adults with early-onset LLD and 23 non-depressed comparisons participated in the study. Participants completed a word list-learning task while undergoing functional magnetic resonance imaging.

RESULTS

In the context of equivalent recall and recognition of words following scanning and similar hippocampal volumes, patients with LLD exhibited less activation in structures known to be relevant for new learning and memory, including hippocampus, parahippocampal gyrus, insula, and cingulate, relative to non-ill comparisons. An important region in which the LLD group displayed greater activation than the non-depressed comparison group was in left inferior frontal gyrus, an area involved in cognitive control and controlled semantic/phonological retrieval and analysis; this region may be critical for LLD patients to consolidate encoded words into memory.

CONCLUSIONS

Functional irregularities found in LLD patients may reflect different modes of processing to-be-remembered information and/or early changes predictive of incipient cognitive decline. Future studies might consider mechanisms that could contribute to these functional differences, including hypothalamic-pituitary-adrenal axis functioning and vascular integrity, and utilize longitudinal designs in order to understand whether functional changes are predictive of incipient cognitive decline.

A systematic review of type 2 diabetes mellitus and hypertension in imaging studies of cognitive aging: time to establish new norms

The rising prevalence of type 2 diabetes (T2DM) and hypertension in older adults, and the deleterious effect of these conditions on cerebrovascular and brain health, is creating a growing discrepancy between the "typical" cognitive aging trajectory and a "healthy" cognitive aging trajectory. These changing health demographics make T2DM and hypertension important topics of study in their own right, and warrant attention from the perspective of cognitive aging neuroimaging research. Specifically, interpretation of individual or group differences in blood oxygenation level dependent magnetic resonance imaging (BOLD MRI) or positron emission tomography (PET H2O(15)) signals as reflective of differences in neural activation underlying a cognitive operation of interest requires assumptions of intact vascular health amongst the study participants. Without adequate screening, inclusion of individuals with T2DM or hypertension in "healthy" samples may introduce unwanted variability and bias to brain and/or cognitive measures, and increase potential for error. We conducted a systematic review of the cognitive aging neuroimaging literature to document the extent to which researchers account for these conditions. Of the 232 studies selected for review, few explicitly excluded individuals with T2DM (9%) or hypertension (13%). A large portion had exclusion criteria that made it difficult to determine whether T2DM or hypertension were excluded (44 and 37%), and many did not mention any selection criteria related to T2DM or hypertension (34 and 22%). Of all the surveyed studies, only 29% acknowledged or addressed the potential influence of intersubject vascular variability on the measured BOLD or PET signals. To reinforce the notion that individuals with T2DM and hypertension should not be overlooked as a potential source of bias, we also provide an overview of metabolic and vascular changes associated with T2DM and hypertension, as they relate to cerebrovascular and brain health.

Factor structure, construct validity, and age- and education-based normative data for the Parametric Go/No-Go Test

The Parametric Go/No-Go (PGNG) test assesses cognitive domains including attention and executive functioning with three levels of increasing difficulty. Level 1 measures accuracy and response time to three targets. Level 2 adds a nonrepeating rule, measuring response time to two targets, accuracy for targets, and accuracy for appropriate inhibition. Level 3 has three targets with the same nonrepeating rule. The task shows good construct validity, and factor analyses show adequate ability to distinguish between processing speed, sustained attention, and inhibition. Normative data for the PGNG, stratified by age and education, as well as strategies for identifying atypical responding, are presented.

Neonatal brain injury and neuroanatomy of memory processing following very preterm birth in adulthood: an fMRI study

Altered functional neuroanatomy of high-order cognitive processing has been described in very preterm individuals (born before 33 weeks of gestation; VPT) compared to controls in childhood and adolescence. However, VPT birth may be accompanied by different types of adverse neonatal events and associated brain injury, the severity of which may have differential effects on brain development and subsequent neurodevelopmental outcome. We conducted a functional magnetic resonance imaging (fMRI) study to investigate how differing degrees of neonatal brain injury, detected by neonatal ultrasounds, affect the functional neuroanatomy of memory processing in VPT young adults. We used a verbal paired associates learning task, consisting of four encoding, four cued-recall and four baseline condition blocks. To further investigate whether differences in neural activation between the groups were modulated by structural brain changes, structural MRI data were also collected. We studied 12 VPT young adults with a history of periventricular haemorrhage with associated ventricular dilatation, 17 VPT individuals with a history of uncomplicated periventricular haemorrhage, 12 individuals with normal ultrasonographic findings, and 17 controls. Results of a linear trend analysis demonstrated that during completion of the paired associates learning task right frontal and right parietal brain activation decreased as the severity of neonatal brain injury increased. There were no statistically significant between-group differences in on-line task performance and participants' intelligence quotient (IQ) at assessment. This pattern of differential activation across the groups was observed particularly in the right middle frontal gyrus during encoding and in the right posterior cingulate gyrus during recall. Structural MRI data analysis revealed that grey matter volume in the right superior temporal gyrus, right cerebellum, left middle temporal gyrus, right globus pallidus and right medial frontal gyrus decreased with increasing severity of neonatal brain injury. However, the significant between-group functional neuroanatomical differences were not directly attributable to the detected structural regional differences.

Neuroanatomical substrates of age-related cognitive decline

There are many reports of relations between age and cognitive variables and of relations between age and variables representing different aspects of brain structure and a few reports of relations between brain structure variables and cognitive variables. These findings have sometimes led to inferences that the age-related brain changes cause the age-related cognitive changes. Although this conclusion may well be true, it is widely recognized that simple correlations are not sufficient to warrant causal conclusions, and other types of correlational information, such as mediation and correlations between longitudinal brain changes and longitudinal cognitive changes, also have limitations with respect to causal inferences. These issues are discussed, and the existing results on relations of regional volume, white matter hyperintensities, and diffusion tensor imaging measures of white matter integrity to age and to measures of cognitive functioning are reviewed. It is concluded that at the current time the evidence that these aspects of brain structure are neuroanatomical substrates of age-related cognitive decline is weak. The final section contains several suggestions concerning measurement and methodology that may lead to stronger conclusions in the future.

Elimination of the enhanced Simon effect for older adults in a three-choice situation: ageing and the Simon effect in a go/no-go Simon task

In a Simon task, participants show better performance when the irrelevant stimulus location corresponds with the response location than when it does not, and this effect is typically greater for older adults than for younger adults. To study the effect of cognitive ageing in the Simon task, we compared young and old adults using two versions of the Simon task: (a) a standard visual Simon task, for which participants respond with left and right key-presses to the red and green colours of stimuli presented in left and right locations; (b) a go/no-go version of the Simon task, which was basically the same, except that the shape of the stimulus in one third of the trials indicates that no response is to be made. In both tasks, both age groups showed the Simon effect. The magnitude of the effect for the standard Simon task was greater for the older adults than for the younger adults. Nevertheless, the two groups showed an equivalent Simon effect in the go/no-go version of the Simon task. Reaction time distribution analyses revealed basically similar functions for both age groups: a decreasing pattern of the Simon effect in the standard task and an increasing pattern of the effect in the go/no-go version of the task. The results suggest that older adults find it more difficult to suppress an automatic activation of the corresponding response, though this automatic activation was reduced in situations where the response was frequently inhibited.

A review of functional brain imaging correlates of successful cognitive aging

Preserved cognitive performance is a key feature of successful aging. Several theoretical models have been proposed to explain the putative underlying relationship between brain function and performance. We aimed to review imaging studies of the association between brain functional response and cognitive performance among healthy younger and older adults to understand the neural correlates of successful cognitive aging. MEDLINE-indexed articles published between January 1989 and December 2009 and bibliographies of these articles and related reviews were searched. Studies that measured brain function with functional magnetic resonance imaging or positron emission tomography, evaluated cognitive performance, analyzed how cognitive performance related to brain response, and studied healthy older individuals were included. Eighty of 550 articles met these criteria. Seventy percent of the studies reported some brain regions in which greater activation related to better cognitive performance among older participants. This association was not universal, however, and was seen mainly in frontal cortex brain response and seemed to be more common among older compared with younger individuals. This review supports the notion of compensatory increases in brain activity in old age resulting in better cognitive performance, as suggested by hemispheric asymmetry reduction and posterior-anterior shift models of functional brain aging. However, a simple model of bigger structure → greater brain response → better cognitive performance might not be accurate. Suggestions for future research are discussed.

Executive function and survival in the context of chronic illness

BACKGROUND

Individual differences in executive function (EF) have been shown to predict risk factors for chronic illness. It is not currently known whether EFs also predict survival time following a diagnosis of a chronic illness.

PURPOSE

The objective of this investigation was to examine the association between individual differences in EF and survival time among individuals suffering from one or more chronic illness.

METHODS

A sample of 162 community-dwelling older adults who suffered from a chronic illness at baseline underwent thorough medical and neurological examinations to ensure freedom from actual or probable dementia. Participants completed cognitive testing and were subsequently followed for 10 years; survival was assessed as survival time over the follow-up interval.

RESULTS

Findings indicated that individual differences in EF predicted survival time, and this association held when adjustments were made for demographic variables (age, sex), education, and body mass index.

CONCLUSION

Individual differences in EF may be important determinants of survival in the context of chronic illness.

Neuroimaging of the developing brain: taking "developing" seriously

With a few notable exceptions, many studies, be they behavioral, neuroimaging, or genetic, are snapshots that compare one child group to one adult group, which capture only two points in time and tell the scientist nothing about the mechanisms underlying neural trajectories over developmental time. Thus, a distinction needs to be drawn between child neuroimaging and developmental neuroimaging, the latter approach being relevant not just to children, but to adults and the ageing brain.

Neural substrates of letter fluency processing in young adults who were born very preterm: alterations in frontal and striatal regions

Several studies have described poorer performance in executive-type tasks in individuals who were born very preterm compared to controls. As there is evidence that high-order executive functions may be underpinned by neuronal activity in frontal-striatal circuits, we investigated with functional MRI a group of young adults who were born very preterm (n=28, gestational age <33 weeks) and controls (n=26) in order to detect possible alterations in brain activation during completion of a letter fluency task with differential cognitive loading ("easy" and "hard" letter trials). Structural MRI data were also collected to clarify whether any functional changes were associated with structural brain volume changes. Group membership, level of task difficulty and gestational age had significant effects on brain activation. In the absence of significant between-group differences in task performance, during "easy" letter trials, very preterm-born individuals showed attenuated activation in anterior cingulate gyrus, right caudate nucleus and left inferior frontal gyrus compared to controls. During "hard" letter trials, very preterm-born individuals showed both decreased and increased BOLD signal compared to controls, in left middle frontal and anterior cingulate gyrus, respectively. BOLD signal in caudate nucleus and anterior cingulate gyrus, in regions with peaks close to areas where between-group differences were observed, was linearly associated with gestational age. Analysis of structural MRI data showed altered grey matter distribution in the preterm-born group compared to controls. However, fMRI results were only partly explained by structural changes, and may reflect processes of functional plasticity for the successful completion of executive-type operations.

Age-related slowing of movement as basal ganglia dysfunction

Attributions of age-related deficits in motor function to structural changes are compromised once the elderly exhibit lower error rates. This is because performance decrements observed in older adults are attributed to inferred strategic preferences for accuracy over speed. To understand genuine age differences in performance, we argue in the following theoretical paper that research needs to resolve methodological shortcomings and account for them within theoretical models of aging. Accounts of aging need to directly manipulate or control strategic differences in performance while assessing structural deficits. When this is done, age-related changes in motor control resemble the intermittencies of control seen in basal ganglia disorders. Given homologous circuitry in the basal ganglia, such observations could generalize to age-related changes in cognitive and emotional processes.

Cognitive neuroscience of aging

The number of reports on the cognitive neuroscience of aging has increased in recent years, and most of these studies have found many similarities in the patterns of activity in young and old adults, indicating that basic neural mechanisms are maintained into older age. Despite these overall similarities, older adults often have less activity in some regions, such as medial temporal areas during memory processing and visual regions across a variety of cognitive domains. It seems clear that age reductions in cognitive function can be tied, at least in part, to these reductions in brain activity. On the other hand, older adults typically also overrecruit some brain areas, mainly the ventral or dorsal prefrontal cortex during memory tasks, as well as both the frontal and parietal regions during tasks engaging cognitive control processes, such as attention. Sometimes this overrecruitment appears to be in response to altered function in other brain regions and is often seen in those older adults who perform better on the task at hand. These findings have provided rather convincing support for the idea that overrecruitment can be compensatory in the elderly. Nevertheless, not all age increases can be interpreted as compensatory, and some are more indicative of neural inefficiency. The challenge facing future research will be to understand the task conditions that promote compensation in older adults, the role of the various brain areas in aiding cognitive function, and how these compensatory mechanisms can be elicited to enhance quality of life in the elderly.

Age-related differences in pain sensitivity and regional brain activity evoked by noxious pressure

Compared with young adults, older people report more chronic pain complaints, and show reduced tolerance to experimental pain. Atrophy of brain parenchyma in normal ageing is well documented, with grey matter reduction occurring across many regions known to be involved in pain processing. However, the functional consequences of these changes, in particular their contribution toward age-related differences in pain perception and report, are yet to be elucidated. The present study investigated the effects of ageing on supraspinal pain processing by comparing regional brain responses to noxious pressure stimulation in 15 young (aged 26+/-3 years) and 15 older (aged 79+/-4 years) adults. Both groups showed significant pain-related activity in a common network of areas including the insula, cingulate, posterior parietal and somatosensory cortices. However, compared with older adults, young subjects showed significantly greater activity in the contralateral putamen and caudate, which could not be accounted for by increased age-associated shrinkage in these regions. The age-related difference in pain-evoked activity seen in the present study may reflect reduced functioning of striatal pain modulatory mechanisms with advancing age.