Bariatric surgery restores visual cortical plasticity in nondiabetic subjects with obesity

The interplay between Hebbian and homeostatic plasticity in the adult visual cortex

Homeostatic and Hebbian plasticity co-operate during the critical period, refining neuronal circuits; however, the interaction between these two forms of plasticity is still unclear, especially in adulthood. Here, we directly investigate this issue in adult humans using two consolidated paradigms to elicit each form of plasticity in the visual cortex: the long-term potentiation-like change of the visual evoked potential (VEP) induced by high-frequency stimulation (HFS) and the shift of ocular dominance induced by short-term monocular deprivation (MD). We tested homeostatic and Hebbian plasticity independently, then explored how they interacted by inducing them simultaneously in a group of adult healthy volunteers. We successfully induced both forms of plasticity: 60 min of MD induced a reliable change in ocular dominance and HFS reliably modulated the amplitude of the P1 component of the VEP. Importantly, we found that, across participants, homeostatic and Hebbian plasticity were negatively correlated, indicating related neural mechanisms, potentially linked to intracortical excitation/inhibition balance. On the other hand, we did not find an interaction when the two forms of plasticity were induced simultaneously. Our results indicate a largely preserved plastic potential in the visual cortex of the adult brain, for both short-term homeostatic and Hebbian plasticity. Crucially, we show for the first time a direct relationship between these two forms of plasticity in the adult human visual cortex, which could inform future research and treatment protocols for neurological diseases. KEY POINTS: Homeostatic and Hebbian plasticity co-operate during the critical period to refine neuronal circuits in the visual cortex. The interaction between these two forms of plasticity is still unknown, especially after the closure of the critical periods and in humans. We directly investigate the interplay between Hebbian and homeostatic visual plasticity in adult humans using non-invasive paradigms. We found a negative correlation between these forms of plasticity showing for the first time a direct relationship between Hebbian and homeostatic plasticity. Our results could inform future research and treatment protocols for neurological diseases.

Obesity Control and Supplementary Nutraceuticals as Cofactors of Brain Plasticity in Multiple Sclerosis Populations

Multiple sclerosis (MS) is an immune-mediated disease characterized by inflammation, demyelination, and neurodegeneration within the central nervous system. Brain plasticity, the brain's ability to adapt its structure and function, plays a crucial role in mitigating MS's impact. This paper explores the potential benefits of lifestyle changes and nutraceuticals on brain plasticity in the MS population. Lifestyle modifications, including physical activity and dietary adjustments, can enhance brain plasticity by upregulating neurotrophic factors, promoting synaptogenesis, and reducing oxidative stress. Nutraceuticals, such as vitamin D, omega-3 fatty acids, and antioxidants like alpha lipoic acid, have shown promise in supporting brain health through anti-inflammatory and neuroprotective mechanisms. Regular physical activity has been linked to increased levels of brain-derived neurotrophic factor and improved cognitive function. Dietary interventions, including caloric restriction and the intake of polyphenols, can also positively influence brain plasticity. Integrating these lifestyle changes and nutraceuticals into the management of MS can provide a complementary approach to traditional therapies, potentially improving neurological outcomes and enhancing the quality of life for the MS population.

Bariatric surgery and diabetes: Current challenges and perspectives

Diabetes mellitus (DM) and obesity have become public issues of global concern. Bariatric surgery for the treatment of obesity combined with type 2 DM has been shown to be a safe and effective approach; however, there are limited studies that have systematically addressed the challenges of surgical treatment of obesity combined with DM. In this review, we summarize and answer the most pressing questions in the field of surgical treatment of obesity-associated DM. I believe that our insights will be of great help to clinicians in their daily practice.

The duration effect of short-term monocular deprivation measured by binocular rivalry and binocular combination

The ocular dominance shift observed after short-term monocular deprivation is a widely used measure of visual homeostatic plasticity in adult humans. Binocular rivalry and binocular combination techniques are used interchangeably to characterize homeostatic plasticity, sometimes leading to contradictory results. Here we directly compare the effect of short-term monocular deprivation on ocular dominance measured by either binocular rivalry or binocular combination and its dependence on the duration of deprivation (15 or 120 min) in the same group of participants. Our results show that both binocular rivalry and binocular combination provide reliable estimates of ocular dominance, which are strongly correlated across techniques both before and after deprivation. Moreover, while 15 min of monocular deprivation induce a larger shift of ocular dominance when measured using binocular combination compared to binocular rivalry, for both techniques, the shift in ocular dominance exhibits a strong dependence on the duration of monocular deprivation, with longer deprivation inducing a larger and longer-lasting shift in ocular dominance. Taken together, our results indicate that both binocular rivalry and binocular combination offer very consistent and reliable measurements of both ocular dominance and the effect short-term monocular deprivation.

Near-Infrared Spectroscopy: A Free-Living Neuroscience Tool to Better Understand Diabetes and Obesity

The human brain is the least accessible of all organs and attempts to study it in vivo rely predominantly on neuroimaging. Functional near-infrared spectroscopy (fNIRS) allows for the study of cortical neural activity in a non-invasive manner that may resemble free-living conditions. Moreover, compared to other neuroimaging tools, fNIRS is less expensive, it does not require the use of ionizing radiation, and can be applied to all study populations (patients suffering from claustrophobia, or neonates). In this narrative review, we provide an overview of the available research performed using fNIRS in patients with diabetes and obesity. The few studies conducted to date have presented controversial results regarding patients with diabetes, some reporting a greater hemodynamic response and others reporting a reduced hemodynamic response compared to the controls, with an unclear distinction between types 1 and 2. Subjects with obesity or a binge eating disorder have reduced prefrontal activation in response to inhibitory food or non-food stimuli; however, following an intervention, such as cognitive treatment, prefrontal activation is restored. Moreover, we discuss the potential of future applications of fNIRS for a better understanding of cortical neural activity in the context of metabolic disorders.

Effect of fasting on short-term visual plasticity in adult humans

Brain plasticity and function is impaired in conditions of metabolic dysregulation, such as obesity. Less is known on whether brain function is also affected by transient and physiological metabolic changes, such as the alternation between fasting and fed state. Here we asked whether these changes affect the transient shift of ocular dominance that follows short-term monocular deprivation, a form of homeostatic plasticity. We further asked whether variations in three of the main metabolic and hormonal pathways affected in obesity (glucose metabolism, leptin signalling and fatty acid metabolism) correlate with plasticity changes. We measured the effects of 2 h monocular deprivation in three conditions: post-absorptive state (fasting), after ingestion of a standardised meal and during infusion of glucagon-like peptide-1 (GLP-1), an incretin physiologically released upon meal ingestion that plays a key role in glucose metabolism. We found that short-term plasticity was less manifest in fasting than in fed state, whereas GLP-1 infusion did not elicit reliable changes compared to fasting. Although we confirmed a positive association between plasticity and supraphysiological GLP-1 levels, achieved by GLP-1 infusion, we found that none of the parameters linked to glucose metabolism could predict the plasticity reduction in the fasting versus fed state. Instead, this was selectively associated with the increase in plasma beta-hydroxybutyrate (B-OH) levels during fasting, which suggests a link between neural function and energy substrates alternative to glucose. These results reveal a previously unexplored link between homeostatic brain plasticity and the physiological changes associated with the daily fast-fed cycle.

Brain effect of bariatric surgery in people with obesity

BACKGROUND/OBJECTIVES

The link between obesity and brain function is a fascinating but still an enigmatic topic. We evaluated the effect of Roux-en-Y gastric bypass (RYGB) on peripheral glucose metabolism, insulin sensitivity, brain glucose utilization and cognitive abilities in people with obesity.

SUBJECTS/METHODS

Thirteen subjects with obesity (F/M 11/2; age 44.4 ± 9.8 years; BMI 46.1 ± 4.9 kg/m²) underwent 75-g OGTT during a [18F]FDG dynamic brain PET/CT study at baseline and 6 months after RYGB. At the same timepoints, cognitive performance was tested with Mini Mental State Examination (MMSE), Montreal Cognitive Assessment (MoCA), Trail making test (TMT) and Token test (TT). Glucose, insulin, C-peptide, GLP-1, GIP, and VIP levels were measured during OGTT. Leptin and BDNF levels were measured before glucose ingestion.

RESULTS

RYGB resulted in significant weight loss (from 46.1 ± 4.9 to 35.3 ± 5.0 kg/m²; p < 0.01 vs baseline). Insulin sensitivity improved (disposition index: from 1.1 ± 0.2 to 2.9 ± 1.1; p = 0.02) and cerebral glucose metabolic rate (CMRg) declined in various brain areas (all p ≤ 0.01). MMSE and MoCA score significantly improved (p = 0.001 and p = 0.002, respectively). TMT and TT scores showed a slight improvement. A positive correlation was found between CMRg change and HOMA-IR change in the caudate nucleus (ρ = 0.65, p = 0.01). Fasting leptin decreased (from 80.4 ± 13.0 to 16.1 ± 2.4 ng/dl; p = 0.001) and correlated with CMRg change in the hippocampus (ρ = 0.50; p = 0.008). CMRg change was correlated with cognitive scores changes on the TMT and TT (all p = 0.04 or less).

CONCLUSIONS

Bariatric surgery improves CMRg directly related to a better cognitive testing result. This study highlights the potential pleiotropic effects of bariatric surgery.

TRIAL REGISTRY NUMBER

NCT03414333.