Frontal and temporal lobe correlates of verbal learning and memory in aMCI and suspected Alzheimer's disease dementia

Odor induced functional connectivity alteration of POC-anterior frontal cortex-medial temporal cortex in patients with mild cognitive impairment

Background

Mild cognitive impairment (MCI) is associated with an increased risk of dementia in older adults. Olfactory impairment may indicate prodromal dementia, yet its underlying mechanisms are not fully understood. This study aimed to investigate the alterations in functional connectivity (FC) of odor-induced olfactory neural circuits in MCI patients.

Methods

The study included 39 MCI patients and 42 normal controls (NCs). All subjects underwent cognitive assessments, olfactory behavior tests, and odor-based functional magnetic resonance imaging (fMRI). Differences in FC within olfactory circuits were analyzed using the generalized psychophysiological interaction (gPPI) method.

Results

Mild cognitive impairment patients showed significant cognitive deficits, including lower scores on the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA), alongside impairments in episodic memory, visuospatial memory, executive function, language, attention, olfactory threshold, and total olfactory function. Compared to NCs, MCI patients exhibited reduced activation in the bilateral primary olfactory cortex (bPOC) during olfactory stimulation. Odor-induced bPOC activation correlated with olfactory thresholds across the cohort. During odor stimulation, MCI patients showed increased FC from the bPOC to the right anterior frontal lobe, particularly the middle frontal gyrus (MFG) and superior frontal gyrus (SFG). Conversely, FC from the right anterior frontal lobe to the medial temporal cortex, including the fusiform and parahippocampal gyri, was reduced in MCI patients. Increased FC from the bPOC to the right SFG/MFG negatively correlated with episodic memory, while decreased FC to the right fusiform/parahippocampal gyri positively correlated with attention, language ability, and olfactory identification.

Conclusion

This study indicates that impaired FC within the primary olfactory cortex (POC)-anterior frontal cortex-medial temporal cortex circuit is a sensitive neuroimaging marker for early MCI identification. The primary dysfunction appears in the POC, suggesting that FC alterations from this region may provide novel diagnostic and therapeutic avenues for early intervention.

Memory consolidation, temporal and parietal atrophy, and metabolism in amyloid-β positive and negative mild cognitive impairment

BACKGROUND

Alzheimer's disease (AD) is classically characterized by alterations in memory consolidation. With the advent of diagnostic biomarkers, some patients clinically diagnosed with AD display biomarkers inconsistent with the diagnosis.

OBJECTIVE

We aimed to explore differences in memory consolidation and neurodegeneration of the temporal and parietal lobes as a function of amyloid-β status in amnestic mild cognitive impairment (aMCI).

METHODS

We examined differences in memory consolidation and neurodegeneration between patients diagnosed with amyloid-β positive aMCI (Aβ+ N = 78), amyloid-β negative aMCI (Aβ- N = 48), and healthy participants (HP; N = 41), within a well-characterized clinical cohort.

RESULTS

Aβ+ exhibited more pronounced consolidation impairments compared to Aβ-, while Aβ- faced more consolidation challenges than HP. Both Aβ+ and Aβ- were similar in hippocampal volume and entorhinal thickness, but Aβ+ had thinner inferior parietal cortex than Aβ-. Using 18F-fluoro-deoxyglucose-positron emission tomography, metabolism in both temporal and parietal regions was lower in Aβ+ relative to Aβ-.

CONCLUSIONS

These findings suggest pathologies other than AD likely contribute to memory consolidation difficulties in aMCI, and neurodegeneration of the parietal cortex in combination with hypometabolism may contribute to more pronounced consolidation problems in Aβ+.

The Neuropsychological Assessment Battery Driving Scenes Test in a Dementia Clinic

OBJECTIVE

In dementia research, the Driving Scenes test from the Neuropsychological Assessment Battery has been shown to relate to memory, dementia diagnosis, and functional impairment. The aim of the current study was to examine Driving Scenes and its component scores, and their relationships with cognition and daily functioning, in a mixed dementia clinic sample.

METHOD

One hundred U.S. military veterans between the ages of 55 and 88 were administered a full neuropsychological protocol that included Driving Scenes.

RESULTS

The Driving Scenes score and its subscores were strongly related to memory skills, and there were additional subscore associations with language and visuospatial functions. Driving Scenes uniquely predicted reported bill payment difficulties and tendency to get lost while driving, which were not predicted by other performances across cognitive domains.

CONCLUSION

Driving Scenes is a clinically and functionally relevant measure of memory. Although the Driving Scenes total score remains useful in dementia evaluations, component scores and error scores contribute additional practical information.

Cortical Thickness Correlates of Go/No-go and Motor Sequencing in Mild Cognitive Impairment and Suspected Alzheimer Disease Dementia

BACKGROUND

While the cognitive hallmark of typical Alzheimer disease (AD) is impaired memory consolidation, increasing evidence suggests that the frontal lobes and associated executive functions are also impacted.

OBJECTIVE

We examined two neurobehavioral executive function tasks and associations with cortical thickness in patients diagnosed with mild cognitive impairment (MCI), suspected AD dementia, and a healthy control group.

METHODS

First, we compared group performances on a go/no-go (GNG) task and on Luria's Fist-Edge-Palm (FEP) motor sequencing task. We then examined correlations between neurobehavioral task performance and the thickness of frontal cortical regions, AD signature regions, broader unbiased brain regions, and white matter hyperintensities (WMH).

RESULTS

Participants with MCI performed worse than healthy controls, but better than participants with suspected AD dementia on both tasks. Both GNG and FEP (to a slightly greater extent) tasks showed diffuse associations with most AD signature regions and multiple additional regions within the temporal, parietal, and occipital cortices. Similarly, both tasks showed significant associations with all other cognitive tasks examined. Of the frontal regions examined, only the middle frontal gyrus and pars opercularis were associated with performance on these tasks. Interactions between the precuneus and transtemporal gyri were most predictive of GNG task performance, while the interaction between superior temporal and lingual gyri was most predictive of FEP task performance.

CONCLUSION

This study replicates difficulties with both GNG and FEP tasks in participants with MCI and AD dementia. Both tasks showed widespread associations with the cortical thickness of various brain structures rather than localizing to frontal regions, consistent with the diffuse nature of AD.

Executive function and cortical thickness in biomarker aMCI

INTRODUCTION

Memory deficits are the primary symptom in amnestic Mild Cognitive Impairment (aMCI); however, executive function (EF) deficits are common. The current study examined EF in aMCI based upon amyloid status (A+/A-) and regional atrophy in signature areas of Alzheimer's disease (AD).

METHOD

Participants included 110 individuals with aMCI (A+ = 66; A- = 44) and 33 cognitively healthy participants (HP). EF was assessed using four neuropsychological assessment measures. The cortical thickness of the AD signature areas was calculated using structural MRI data.

RESULTS

A + had greater EF deficits and cortical atrophy relative to A - in the supramarginal gyrus and superior parietal lobule. A - had greater EF deficits relative to HP, but no difference in signature area cortical thickness.

DISCUSSION

The current study found that the degree of EF deficits in aMCI are a function of amyloid status and cortical thinning in the parietal cortex.

More Similar than Different: Memory, Executive Functions, Cortical Thickness, and Glucose Metabolism in Biomarker-Positive Alzheimer's Disease and Behavioral Variant Frontotemporal Dementia

Background

Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) are typically associated with very different clinical and neuroanatomical presentations; however, there is increasing recognition of similarities.

Objective

To examine memory and executive functions, as well as cortical thickness, and glucose metabolism in AD and bvFTD signature brain regions.

Methods

We compared differences in a group of biomarker-defined participants with Alzheimer's disease and a group of clinically diagnosed participants with bvFTD. These groups were also contrasted with healthy controls (HC).

Results

As expected, memory functions were generally more impaired in AD, followed by bvFTD, and both clinical groups performed more poorly than the HC group. Executive function measures were similar in AD compared to bvFTD for motor sequencing and go/no-go, but bvFTD had more difficulty with a set shifting task. Participants with AD showed thinner cortex and lower glucose metabolism in the angular gyrus compared to bvFTD. Participants with bvFTD had thinner cortex in the insula and temporal pole relative to AD and healthy controls, but otherwise the two clinical groups were similar for other frontal and temporal signature regions.

Conclusions

Overall, the results of this study highlight more similarities than differences between AD and bvFTD in terms of cognitive functions, cortical thickness, and glucose metabolism. Further research is needed to better understand the mechanisms mediating this overlap and how these relationships evolve longitudinally.

Surface-based correlates of cognition along the Alzheimer's continuum in a memory clinic population

Composite cognitive measures in large-scale studies with biomarker data for amyloid and tau have been widely used to characterize Alzheimer's disease (AD). However, little is known about how the findings from these studies translate to memory clinic populations without biomarker data, using single measures of cognition. Additionally, most studies have utilized voxel-based morphometry or limited surface-based morphometry such as cortical thickness, to measure the neurodegeneration associated with cognitive deficits. In this study, we aimed to replicate and extend the biomarker, composite study relationships using expanded surface-based morphometry and single measures of cognition in a memory clinic population. We examined 271 clinically diagnosed symptomatic individuals with mild cognitive impairment (N = 93) and Alzheimer's disease dementia (N = 178), as well as healthy controls (N = 29). Surface-based morphometry measures included cortical thickness, sulcal depth, and gyrification index within the "signature areas" of Alzheimer's disease. The cognitive variables pertained to hallmark features of Alzheimer's disease including verbal learning, verbal memory retention, and language, as well as executive function. The results demonstrated that verbal learning, language, and executive function correlated with the cortical thickness of the temporal, frontal, and parietal areas. Verbal memory retention was correlated to the thickness of temporal regions and gyrification of the inferior temporal gyrus. Language was related to the temporal regions and the supramarginal gyrus' sulcal depth and gyrification index. Executive function was correlated with the medial temporal gyrus and supramarginal gyrus sulcal depth, and the gyrification index of temporal regions and supramarginal gyrus, but not with the frontal areas. Predictions of each of these cognitive measures were dependent on a combination of structures and each of the morphometry measurements, and often included medial temporal gyrus thickness and sulcal depth. Overall, the results demonstrated that the relationships between cortical thinning and cognition are widespread and can be observed using single measures of cognition in a clinically diagnosed AD population. The utility of sulcal depth and gyrification index measures may be more focal to certain brain areas and cognitive measures. The relative importance of temporal, frontal, and parietal regions in verbal learning, language, and executive function, but not verbal memory retention, was replicated in this clinic cohort.

Patterns of proactive interference in CVLT-II: evidence of a low-organized, disorganized, and highly organized learning style

OBJECTIVE

Previous studies have interpreted proactive interference (PI) either as indicating executive dysfunction or a normal process indicating deep level encoding. We investigated these competing models of PI in a large clinical sample using cluster analyses. We expected to find clusters defined by high PI but otherwise characterized by either EF impairment or of good memory performance.

METHOD

File records of 731 patients with neurological or psychiatric disorders were analyzed. PI-scores, false positive recognition errors, and semantic organization scores on the California Verbal Learning Test-II (CVLT-II) were subjected to cluster analyses. Clusters were compared regarding buildup and release from PI, memory performance and strategy measures, measures of intelligence, EF, and processing speed.

RESULTS

The analyses revealed six analyzable clusters. Two clusters showed no buildup of PI and normal release from PI. Discriminability was impaired both in List A and B. Learning acquisition and speeded measures of EF were reduced. One cluster showed both buildup of PI and problems with releasing from PI, and particularly impaired discriminability of List B. Semantic organization was low. Learning consolidation and EF speeded measures were impaired. Two other clusters showed buildup of PI, but no problem with release. Learning was highly organized, and they showed good memory and normal neuropsychological performance.

CONCLUSIONS

Results shows differentiation between a low organized EF dysfunction pattern with no PI, a disorganized PI pattern also indicating EF dysfunction and a highly organized pattern where PI seems to be the price to pay for high effort put into the learning process.

The effects of deep transcranial magnetic stimulation on Alzheimer's disease: a case report examining cognitive functioning, memory, and QEEG

Numerous treatment options are being studied for Alzheimer's disease (AD) given the rising prevalence of this condition worldwide. Transcranial Magnetic Stimulation (TMS) is a promising option for regulating specific neurological abnormalities pertaining to this condition. This case presents a patient with AD and co-occurring major depressive disorder that received 36 sessions of Deep TMS to the frontal and temporal lobes. This patient experienced improved general cognitive functioning and memory, remission from depression, and reduced slow-frequency theta activity in frontal and temporal sites. Following 7 months of weekly maintenance, additional improvements occurred. This report suggests that Deep TMS may be effective in mitigating AD symptoms, and maintenance sessions are advisable.