Olfactory hallucinations as primary symptom for ischemia in the right posterior insula

Uncovering Interoceptive Human Insular Lobe Function through Intraoperative Cortical Stimulation-A Review

The insular cortex, a critical hub in the brain's sensory, cognitive, and emotional networks, remains an intriguing subject of study. In this article, we discuss its intricate functional neuroanatomy, emphasizing its pivotal role in processing olfactory information. Through concise exploration, we delve into the insula's diverse connectivity and its involvement in sensory integration, particularly in olfaction. Stimulation studies in humans reveal compelling insights into the insula's contribution to the perception of smell, hinting at its broader implications for cognitive processing. Additionally, we explore an avenue of research in which studying olfactory processing via insular stimulation could unravel higher-level cognitive processes. This innovative approach could help give a fresh perspective on the interplay between sensory and cognitive domains, offering valuable insights into the neural mechanisms underlying cognition and emotion. In conclusion, future research efforts should emphasize a multidisciplinary approach, combining advanced imaging and surgical techniques to explore the intricate functions of the human insula. Moreover, awake craniotomies could offer a unique opportunity for real-time observation, shedding light on its neural circuitry and contributions to higher-order brain functions. Furthermore, olfaction's direct cortical projection enables precise exploration of insular function, promising insights into cognitive and emotional processes. This multifaceted approach will deepen our understanding of the insular cortex and its significance in human cognition and emotion.

The insula: Leveraging cellular and systems-level research to better understand its roles in health and schizophrenia

Schizophrenia is a highly heterogeneous disorder characterized by a multitude of complex and seemingly non-overlapping symptoms. The insular cortex has gained increasing attention in neuroscience and psychiatry due to its involvement in a diverse range of fundamental human experiences and behaviors. This review article provides an overview of the insula's cellular and anatomical organization, functional and structural connectivity, and functional significance. Focusing on specific insula subregions and using knowledge gained from humans and preclinical studies of insular tracings in non-human primates, we review the literature and discuss the functional roles of each subregion, including in somatosensation, interoception, salience processing, emotional processing, and social cognition. Building from this foundation, we then extend these findings to discuss reported abnormalities of these functions in individuals with schizophrenia, implicating insular involvement in schizophrenia pathology. This review underscores the insula's vast role in the human experience and how abnormal insula structure and function could result in the wide-ranging symptoms observed in schizophrenia.

Patterns of Gray and White Matter Volume Alterations in Patients With Post-Traumatic Anosmia: A Voxel-Based Morphometry Study

Objective

Traumatic brain injury is one of the major causes of human olfactory dysfunction and leads to brain structure alterations, mainly in the cortical olfactory regions. Our study aimed to investigate volume changes in the gray matter (GM) and white matter (WM) in patients with post-traumatic anosmia and then to explore the relationship between GM volume and olfactory function.

Methods

Ethics committee approved prospective studies which included 22 patients with post-traumatic anosmia and 18 age- and gender-matched healthy volunteers. Olfactory function was assessed using the Sniffin' Sticks. High-resolution 3-dimensional T1 MRIs of the participants were acquired on a 3T scanner and the data were collected for voxel-based morphometry (VBM) analysis. Furthermore, the GM and WM volumes of the whole brain regions were compared and correlated with olfactory function.

Results

The analysis revealed significant GM volume reduction in the orbitofrontal cortex (OFC), gyrus rectus (GR), olfactory cortex, insula, parahippocampal, temporal pole, and cerebellum (all P < 0.001) in patients. Besides, WM volume loss was also found in the OFC, GR, and insula (all P < 0.001) in patients. All WM atrophy areas were connected to areas of GM volume loss spatially. Correlation analysis showed the olfactory scores were significantly positively correlated with the GM volume of the occipital cortex (P < 0.001, and PFWE < 0.05), while no significant correlation was found between the Sniffin' Sticks test scores and the WM volume in patients.

Conclusion

The reduction of GM and WM volume in olfactory-related regions was responsible for olfactory dysfunction in post-traumatic patients. The occipital cortex may play a compensation mechanism to maintain the residual olfactory function. To our knowledge, we report here for the first time on white matter volume alterations specifically in post-traumatic patients with anosmia.

Insula and Olfaction: A Literature Review and Case Report

(1) Background: It is well established that the insula is involved in olfaction, though its specific role in olfactory processing remains uncertain. In this paper, we first review the current literature on the insula and olfaction. Then, we describe the case of a 56-year-old man with a left insular cavernoma that caused olfactory disturbances. (2) Results: Structural neuroimaging studies suggest that insular gray matter volume is related to olfactory function, and functional neuroimaging shows that various types of stimuli lead to either lateralized or bilateral insular activations. Studies using electro-cortical stimulation reveal a specific region of the insular cortex, around the central insular sulcus, that could be related to unpleasant odor processing. Previous cases of insular lesions leading to olfactory disturbances suggest that left-sided insular lesions may more frequently lead to olfactory changes. In our patient with a left insular cavernoma, odors that were previously perceived as pleasant started smelling unpleasant and were hard to distinguish. Despite these subjective complaints, olfactory function assessed with the Sniffin’ Sticks test was normal. (3) Conclusions: Current tests may not be sensitive to all types of olfactory impairments associated with insular damage, and further studies should be conducted to develop olfactory tests assessing the hedonic appreciation of odors.

Phantosmia as the first presentation of a cavernous sinus - clinoidal meningioma

Cavernous sinus meningiomas (CSM) are complex skull base lesions that, due to their particular anatomical location, render surgical management difficult. Their symptomatology is versatile, and the clinical outcome is difficult to predict. We present the case of a 57-year old female patient who experienced phantosmia - an abnormal, persistent, olfactory sensation of cigarette smell for 18 months. MRI was performed and revealed a left cavernous sinus meningioma, extending into the left temporal fossa, with olfactory and optic nerve distortion. To our knowledge, this is the first reported case of phantosmia as the initial presentation of a lesion in the cavernous sinus.

Adaptive and maladaptive neural compensatory consequences of sensory deprivation-From a phantom percept perspective

It is suggested that the brain undergoes plastic changes in order to adapt to changing environmental needs. Sensory deprivation results in decreased input to the brain leading to adaptive or maladaptive changes. Although several theories hypothesize the mechanism of these adaptive and maladaptive changes, the course of action taken by the brain heavily depends on the age of incidence of damage. The growing body of literature on the topic proposes that maladaptive changes in the brain are instrumental in creating phantom percepts, defined as the perception of a sensory experience in the absence of a physical stimulus. The current article reviews the mechanisms of adaptive and maladaptive plasticity in the brain in congenital, early, and late-onset sensory deprivation in conjunction with the phantom percepts in the different sensory domains. We propose that the mechanisms of adaptive and maladaptive plasticity fall under a universal construct of updating hierarchical Bayesian prediction errors. This theory of the Bayesian brain hypothesizes that the brain constantly compares its internal milieu with changing environmental cues and either adjusts its predictions or discards the change, depending on the novelty or salience of the external stimulus. We propose that adaptive plasticity reflects both successful bottom-up compensation and top-down updating of the model while maladaptive plasticity reflects failure in one or both mechanisms, resulting in a constant prediction-error. Finally, we hypothesize that phantom percepts are generated by the brain as a solution to this prediction error and are thus a manifestation of unsuccessful adaptation to sensory deprivation.

Enhancement of angiogenic effects by hypoxia-preconditioned human umbilical cord-derived mesenchymal stem cells in a mouse model of hindlimb ischemia

It has been studied that mesenchymal stem cells (MSCs) have the capability to promote angiogenesis. Furthermore, there is strong evidence that hypoxic conditions can enhance angiogenesis and immune modulation mediated by MSCs, a notion that has been applied in many fields of clinical application. In the present study, we compared the efficacy of hypoxia preconditioned human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) and normoxia conditioned hUC-MSCs for the treatment of ischemic injury in hindlimbs of an immunodeficient mouse model. Expression of negative markers for MSC such as CD31, CD34, and CD45 or positive markers such as CD44, CD73, CD90, and CD105 was not significantly changed in hypoxia preconditioned hUC-MSCs compared with hUC-MSCs cultured in normoxic condition. Expression of angiogenesis-related genes such as COX-2, VEGF, Tie-2, and TGF-β1 was increased compared with hUC-MSCs cultured in normoxic conditions. In the in vivo model, CD31 expression as a marker of angiogenesis was significantly increased in the ischemic limbs at 1 month after injection with hypoxic hUC-MSCs. Angiogenesis-related genes such as Ang-1, COX-1, PIGF, and MCP-1 were significantly upregulated in the muscle of ischemic hindlimbs treated with hypoxic hUC-MSCs than normoxic hUC-MSCs. Expression of proinflammatory genes such as IL-1, and IL-20 was reduced, whereas TGF-β1, which has an anti-inflammatory effect, was strongly increased. In conclusion, hypoxic culture conditions could induce expression of angiogenesis related genes in hUC-MSCs, and hypoxia preconditioned hUC-MSCs showed enhancing effects by inducing angiogenesis and low inflammatory immune response compared with normoxic hUC-MSCs in the ischemia injured hindlimb of immunodeficient mice.