Higher-Order Inputs Involved in Appetite Control

The understanding of the neural control of appetite sheds light on the pathogenesis of eating disorders such as anorexia nervosa and obesity. Both diseases are a result of maladaptive eating behaviors (overeating or undereating) and are associated with life-threatening health problems. The fine regulation of appetite involves genetic, physiological, and environmental factors, which are detected and integrated in the brain by specific neuronal populations. For centuries, the hypothalamus has been the center of attention in the scientific community as a key regulator of appetite. The hypothalamus receives and sends axonal projections to several other brain regions that are important for the integration of sensory and emotional information. These connections ensure that appropriate behavioral decisions are made depending on the individual's emotional state and environment. Thus, the mechanisms by which higher-order brain regions integrate exteroceptive information to coordinate feeding is of great importance. In this review, we will focus on the functional and anatomical projections connecting the hypothalamus to the limbic system and higher-order brain centers in the cortex. We will also address the mechanisms by which specific neuronal populations located in higher-order centers regulate appetite and how maladaptive eating behaviors might arise from altered connections among cortical and subcortical areas with the hypothalamus.

Resting-state functional abnormalities in ischemic stroke: a meta-analysis of fMRI studies

Ischemic stroke is a leading neurological cause of severe disabilities and death in the world and has a major negative impact on patients' quality of life. However, the neural mechanism of spontaneous fluctuating neuronal activity remains unclear. This meta-analysis explored brain activity during resting state in patients with ischemic stroke including 22 studies of regional homogeneity, amplitude of low-frequency fluctuation, and fractional amplitude of low-frequency fluctuation (692 patients with ischemic stroke, 620 healthy controls, age range 35-80 years, 41% female, 175 foci). Results showed decreased regional activity in the bilateral caudate and thalamus and increased regional activity in the left superior occipital gyrus and left default mode network (precuneus/posterior cingulate cortex). Meta-analysis of the amplitude of low-frequency fluctuation studies showed that increased activity in the left inferior frontal gyrus was reduced across the progression from acute to chronic phases. These findings may indicate that disruption of the subcortical areas and default mode network could be one of the core functional abnormalities in ischemic stroke. Altered brain activity in the inferior frontal gyrus could be the imaging indicator of brain recovery/plasticity after stroke damage, which offers potential insight into developing prediction models and therapeutic strategies for ischemic stroke rehabilitation and recovery.

Alterations in functional connectivity of interoceptive and Cortico-Subcortical areas in Multiple Sclerosis-Related fatigue

Fatigue in people with Multiple Sclerosis (PwMS) is a poorly understood, complex, and disabling symptom. We hypothesized that the perception of fatigue in PwMS results from increased information processing in cortical areas responsible for the perception of bodily states and decreased information processing in the cortico-basal ganglia network involved in the perception of motor performance. We investigated whether PwMS who perceive excessive fatigue would have increased resting-state functional connectivity (rsFC) between interoceptive brain areas (amygdala, anterior cingulate cortex [ACC], and insula) and decreased rsFC between cortico-basal ganglia premotor network compared to PwMS not reporting fatigue. Twenty-three relapsing-remitting PwMS were divided into fatigued versus non-fatigued groups based on the Modified Fatigue Impact Scale score (≥38 points). Age-matched healthy controls (n = 21) were also analyzed. All the participants underwent resting-state functional magnetic resonance imaging. PwMS who perceived abnormal fatigue, compared to non-fatigued PwMS, showed reduced rsFC between cortico-basal ganglia network and increased rsFC within interoceptive brain areas (amygdala, ACC, and insula) involved in perception of bodily states (P ≤ 0.01). Increased rsFC within interoceptive brain areas was specific for fatigued PwMS as this result did not appear when comparing PwMS (fatigued and non-fatigued) with healthy controls. The Modified Fatigue Impact Scale scores were correlated with the increased rsFC between interoceptive brain areas (amygdala and insula) and decreased rsFC between cortico-basal ganglia (P < 0.01). MS-related perceived fatigue has a central cause, and it may be due to increased interoceptive brain activity (perception of bodily states). Interventions are needed to decrease fatigue and reorganize the brain circuitry.

Sub-cortical areas process physical size but not numerical value

A robust finding in the numerical cognition literature is that the physical size and the numerical value of two to-be-compared digits interact, resulting in a size congruity effect (SiCE). The current study focuses on the possible role of prestriate areas in a digit comparison Stroop-like task. In the visual pathway, prestriate areas refer to regions from the retina up to the primary visual cortex (V1). I hypothesized that processing of physical size, but not numerical value, begins already in prestriate areas. This is because physical size is a basic visual feature while the numerical value of a symbol is a learned convention that should be retrieved from long-term memory. Adult participants compared the size or the numerical value of two digits. Without participants' awareness, I projected the digits either to the same eye, or each digit to a different eye. The latter type of presentation prevents prestriate areas from taking part in comparing the digits. Therefore, slower a response time under this condition hints at the involvement of prestriate areas. Evidence confirmed the initial hypothesis, demonstrating slower performance when the stimuli are segregated between the eyes but only for physical size comparisons. This finding suggests that at least the initial processing of physical size, when relevant, is done before, and by different neural substrate than numerical value. The implications of the study and future directions are discussed.