Brain Events Underlying Episodic Memory Changes in Aging: A Longitudinal Investigation of Structural and Functional Connectivity

Fjell, Anders M.; Sneve, Markus Handal; Storsve, Andreas Berg; Grydeland, Håkon; Yendiki, Anastasia; Walhovd, Kristine B.

doi:10.1093/cercor/bhv102

Cited by 116 publications

(111 citation statements)

References 102 publications

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“…In addition, we found a correlation between the episodic memory measure of list learning with the left volume of the hippocampus across all subjects, suggesting evidence for this impairment to be reflected in the volumetric structure of the hippocampus, which is similarly supported by other studies [79, 80]. There was also a relationship between cognitive impairment in several episodic memory measures and worse gray matter subcortical integrity in both the caudate and hippocampus, also providing support for microstructural abnormalities in these structures to be related to cognitive impairment.…”

Section: Discussionsupporting

confidence: 89%

Altered Microstructural Caudate Integrity in Posttraumatic Stress Disorder but Not Traumatic Brain Injury

et al. 2017

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ObjectiveGiven the high prevalence and comorbidity of combat-related PTSD and TBI in Veterans, it is often difficult to disentangle the contributions of each disorder. Examining these pathologies separately may help to understand the neurobiological basis of memory impairment in PTSD and TBI independently of each other. Thus, we investigated whether a) PTSD and TBI are characterized by subcortical structural abnormalities by examining diffusion tensor imaging (DTI) metrics and volume and b) if these abnormalities were specific to PTSD versus TBI.MethodWe investigated whether individuals with PTSD or TBI display subcortical structural abnormalities in memory regions by examining DTI metrics and volume of the hippocampus and caudate in three groups of Veterans: Veterans with PTSD, Veterans with TBI, and Veterans with neither PTSD nor TBI (Veteran controls).ResultsWhile our results demonstrated no macrostructural differences among the groups in these regions, there were significant alterations in microstructural DTI indices in the caudate for the PTSD group but not the TBI group compared to Veteran controls.ConclusionsThe result of increased mean, radial, and axial diffusivity, and decreased fractional anisotropy in the caudate in absence of significant volume atrophy in the PTSD group suggests the presence of subtle abnormalities evident only at a microstructural level. The caudate is thought to play a role in the physiopathology of PTSD, and the habit-like behavioral features of the disorder could be due to striatal-dependent habit learning mechanisms. Thus, DTI appears to be a vital tool to investigate subcortical pathology, greatly enhancing the ability to detect subtle brain changes in complex disorders.

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Section: Discussionsupporting

confidence: 89%

Altered Microstructural Caudate Integrity in Posttraumatic Stress Disorder but Not Traumatic Brain Injury

et al. 2017

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“…The right cingulum angular bundle runs along the inferior cingulum and connects frontal to hippocampal and para-hippocampal regions (Schmahmann et al 2007). Given that chronic cannabis use is associated with worsening verbal memory (Solowij and Battisti 2008;Broyd et al 2015), and poorer integrity of the cingulum angular bundle is also associated with poorer memory in both younger and older adults (Fjell et al 2015;Ezzati et al 2015), our findings may provide further evidence for impairment in the memory systems of chronic cannabis users.…”

Section: Discussionmentioning

confidence: 58%

An MRI study of white matter tract integrity in regular cannabis users: effects of cannabis use and age

et al. 2016

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Rationale Conflicting evidence exists on the effects of cannabis use on brain white matter integrity. The extant literature has exclusively focused on younger cannabis users, with no studies sampling older cannabis users. Objectives We recruited a sample with a broad age range to examine the integrity of major white matter tracts in association with cannabis use parameters and neurodevelopmental stage. Methods Regular cannabis users (n = 56) and non-users (n = 20) with a mean age of 32 (range 18-55 years) underwent structural and diffusion MRI scans. White matter was examined using voxel-based statistics and via probabilistic tract reconstruction. The integrity of tracts was assessed using average fractional anisotropy, axial diffusivity and radial diffusivity. Diffusion measures were compared between users and non-users and as group-by-age interactions. Correlations between diffusion measures and age of onset, duration, frequency and dose of current cannabis use were examined. Results Cannabis users overall had lower fractional anisotropy than healthy non-users in the forceps minor tract only (p = .015, partial eta = 0.07), with no voxel-wise differences observed. Younger users showed predominantly reduced axial diffusivity, whereas older users had higher radial diffusivity in widespread tracts. Higher axial diffusivity was associated with duration of cannabis use in the cingulum angular bundle (beta = 5.00 x 10−5, p = .003). Isolated higher AD in older cannabis users was also observed. Conclusions The findings suggest that exogenous cannabinoids alter normal brain maturation, with differing effects at various neurodevelopmental stages of life. These age-related differences are posited to account for the disparate results described in the literature.

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“…Previous studies showed that several striatal subregions (especially caudate) and the hippocampus interact during episodic memory (41)(42)(43)(44)(45)(46), and considerable overlap has been observed in the pattern of functional connectivity for hippocampal and caudate seeds (47). This suggests that these regions are part of a shared functional network.…”

Section: Discussionmentioning

confidence: 94%

Dopamine D2 receptor availability is linked to hippocampal–caudate functional connectivity and episodic memory

Nyberg

Karalija

Salami

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

144

131

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D1 and D2 dopamine receptors (D1DRs and D2DRs) may contribute differently to various aspects of memory and cognition. The D1DR system has been linked to functions supported by the prefrontal cortex. By contrast, the role of the D2DR system is less clear, although it has been hypothesized that D2DRs make a specific contribution to hippocampus-based cognitive functions. Here we present results from 181 healthy adults between 64 and 68 y of age who underwent comprehensive assessment of episodic memory, working memory, and processing speed, along with MRI and D2DR assessment with [ 11 C]raclopride and PET. Caudate D2DR availability was positively associated with episodic memory but not with working memory or speed. Whole-brain analyses further revealed a relation between hippocampal D2DR availability and episodic memory. Hippocampal and caudate D2DR availability were interrelated, and functional MRIbased resting-state functional connectivity between the ventral caudate and medial temporal cortex increased as a function of caudate D2DR availability. Collectively, these findings indicate that D2DRs make a specific contribution to hippocampus-based cognition by influencing striatal and hippocampal regions, and their interactions.dopamine | memory | hippocampus D opamine (DA) plays a key role in several cognitive processes (1-4). Reductions of D1 and D2 DA receptors (D1DRs and D2DRs) in aging (5-7) have been linked to agerelated cognitive deficits (8, 9). The D1DR system has been related to functions supported by the prefrontal cortex (PFC), such as working memory and executive functions (10-12), which may reflect the relatively high density of D1DRs in the PFC (13). However, the role of D2DRs is far less clear. D2DRs are present in the PFC at very low densities (13), and evidence supporting a role for the D2DR system in working memory and executive functions is elusive (10). Pharmacological (14, 15) and PET studies assessing striatal D2DR availability (or binding potential to nondisplacable tissue uptake; BP ND ) with [ 11 C]raclopride (16, 17) have yielded mixed findings in relation to cognition. It has been hypothesized that D2DRs make a specific contribution to hippocampus-based cognitive functions (10,18,19). Supporting these claims, positive links between D2DR BP ND and episodic memory are commonly observed (20-23). PET imaging of hippocampal D2DR BP ND also provides support for this hypothesis, although some studies indicate that hippocampal D2DRs may be related to both episodic memory and PFC-based executive functions (22, 23), including verbal working memory (24). Medial temporal lobe regions have been implicated in working memory (25,26), and D2DR-mediated modulation may be exerted via hippocampal-cortical pathways (27). In addition, a [ 11 C]raclopride task-activation PET study demonstrated contributions of striatal D2DRs to a verbal working-memory task (11).Taken together, the specific role of the D2DR system in cognition remains unclear, likely due to the fact that past studies included small and age-hetero...

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Brain Events Underlying Episodic Memory Changes in Aging: A Longitudinal Investigation of Structural and Functional Connectivity

Cited by 116 publications

References 102 publications

Altered Microstructural Caudate Integrity in Posttraumatic Stress Disorder but Not Traumatic Brain Injury

Altered Microstructural Caudate Integrity in Posttraumatic Stress Disorder but Not Traumatic Brain Injury

An MRI study of white matter tract integrity in regular cannabis users: effects of cannabis use and age

Dopamine D2 receptor availability is linked to hippocampal–caudate functional connectivity and episodic memory

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