Clear and Consistent Imaging of Hippocampal Internal Architecture With High Resolution Multiple Image Co-registration and Averaging (HR-MICRA)

Effects of a brief HIIT intervention on cognitive performance in older women

Cardiorespiratory fitness (CRF) mitigates age-related decline in cognition and brain volume. Little is known, however, about the effects of high-intensity interval training (HIIT) on cognitive aging and the relationship between HIIT, cognition, hippocampal subfield volumes, and cerebral oxygen extraction fraction (OEF). Older sedentary women participated in an 8-week HIIT intervention. We conducted cognitive assessments, fitness assessments (VO2max), MRI scans: asymmetric spin echo oxygen extraction fraction (ASE-OEF), high-resolution multiple image co-registration and averaging (HR-MICRA) imaging, and transcranial Doppler ultrasonography before and after the intervention. VO2max increased from baseline (M = 19.36, SD = 2.84) to follow-up (M = 23.25, SD = 3.61), Z =  - 2.93, p < .001, r = 0.63. Composite cognitive (Z =  - 2.05, p = 0.041), language (Z =  - 2.19, p = 0.028), and visuospatial memory (Z =  - 2.22, p = 0.026), z-scores increased significantly. Hippocampal subfield volumes CA1 and CA3 dentate gyrus and subiculum decreased non-significantly (all p > 0.05); whereas a significant decrease in CA2 (Z =  - 2.045, p = 0.041, r = 0.436) from baseline (M = 29.51; SD = 24.50) to follow-up (M = 24.50; SD = 13.38) was observed. Right hemisphere gray matter was correlated with language z-scores (p = 0.025; r = 0.679). The subiculum was correlated with attention (p = 0.047; r = 0.618) and verbal memory (p = 0.020; r = 0.700). The OEF and CBF were unchanged at follow-up (all p > .05). Although we observed cognitive improvements following 8 weeks of our HIIT intervention, they were not explained by hippocampal, OEF, or CBF changes.

Development of an objective method to quantify hippocampal dentation

Hippocampal dentation (HD) refers to a series of ridges (dentes) seen on the inferior aspect of the hippocampus. The degree of HD varies dramatically across healthy individuals, and hippocampal pathology may result in loss of HD. Existing studies show associations between HD and memory performance in healthy adults as well as temporal lobe epilepsy (TLE) patients. However, until now studies relied on visual assessment of HD as no objective methods to quantify HD have been described. In this work, we describe a method to objectively quantify HD by transforming the characteristic 3D surface morphology of HD into a simplified 2D plot for which area under the curve (AUC) was calculated. This was applied to T1w scans of 59 TLE subjects, each with one epileptic hippocampus and one normal appearing hippocampus. Results showed that AUC significantly correlated with the number of dentes based on visual inspection (p < .05) and correctly sorted a set of hippocampi from least to most prominently dentated. Intra- and inter-rater reliability was nearly perfect (ICC ≥ 0.99). AUC values were significantly lower in epileptic hippocampi compared to contralateral hippocampi (p = .00019), consistent with previously published findings. In the left TLE group, the AUC values from the contralateral hippocampi showed a positive trend (p = .07) with verbal memory acquisition scores but was not statistically significant. The proposed approach is the first objective, quantitative measurement of dentation described in the literature. The AUC values numerically capture the complex surface contour information of HD and will enable future study of this interesting morphologic feature.

Loss of hippocampal dentation in hippocampal sclerosis and its relationship to memory dysfunction

OBJECTIVE

Hippocampal dentation (HD) is a "tooth-like" morphological feature observed on the inferior aspect of the human hippocampus. It has been found that HD varies dramatically in healthy adults and is positively associated with verbal and visual memory. In this work, we evaluate the loss of HD and its association to memory dysfunction in patients with temporal lobe epilepsy who have hippocampal sclerosis (HS).

METHODS

58 unilateral HS patients with neuropsychological data were identified from a retrospective database. T1w MPRAGE images (~1mm resolution) were upsampled to 0.25mm and were processed using ASHS software to obtain ultra high resolution segmentations and 3D renderings. Dentes were counted on the epileptic and contralateral sides, and associations were tested between dentation on the epileptic versus contralateral sides and measures of verbal and visuospatial memory with respect to the dominant versus non-dominant hemisphere.

RESULTS

The median number of dentes in epileptic hippocampi was significantly lower than in contralateral hippocampi (p<0.0001). Among cases with HS in the dominant hemisphere, verbal memory was significantly correlated with contralateral non-dominant hemisphere dentation (r = 0.45, p = 0.02). Similarly, among cases of HS in the non-dominant hemisphere, visual memory was significantly correlated with contralateral dominant hemisphere dentation (r = 0.50, p = 0.03). All other analyses were not significant.

SIGNIFICANCE

This is the first study characterizing dentation in TLE patients with HS and its memory correlates. There is marked loss of dentation in sclerotic hippocampi compared to the unaffected contralateral hippocampi. Material-specific measures of memory performance are paradoxically correlated with dentation contralateral to the side with HS, suggesting that contralateral functional capacity explains some of the variation in memory across TLE patients. Hippocampal dentation is an important variable to consider in understanding memory loss in TLE.

Recent Advances in Neuroimaging of Epilepsy

Human neuroimaging has had a major impact on the biological understanding of epilepsy and the relationship between pathophysiology, seizure management, and outcomes. This review highlights notable recent advancements in hardware, sequences, methods, analyses, and applications of human neuroimaging techniques utilized to assess epilepsy. These structural, functional, and metabolic assessments include magnetic resonance imaging (MRI), positron emission tomography (PET), and magnetoencephalography (MEG). Advancements that highlight non-invasive neuroimaging techniques used to study the whole brain are emphasized due to the advantages these provide in clinical and research applications. Thus, topics range across presurgical evaluations, understanding of epilepsy as a network disorder, and the interactions between epilepsy and comorbidities. New techniques and approaches are discussed which are expected to emerge into the mainstream within the next decade and impact our understanding of epilepsies. Further, an increasing breadth of investigations includes the interplay between epilepsy, mental health comorbidities, and aberrant brain networks. In the final section of this review, we focus on neuroimaging studies that assess bidirectional relationships between mental health comorbidities and epilepsy as a model for better understanding of the commonalities between both conditions.