The Cerebellum in Emotions and Psychopathology

Dennis J.L.G. Schutter, Dennis Schutter

• Publisher: Routledge
• Year: 2020
• eBook ISBN: 9781351383745
• Topic: Psychology
• Subtopic: Cognitive Psychology & Cognition
• Index: Psychology

This groundbreaking volume examines the complex role of the cerebellum in emotional regulation and disorders that are insufficiently understood, subverting the widely held belief that the cerebellum is solely involved in balance and motor functions.

Beginning with the evolution of the cerebellum toward a structure dedicated to homeostatic regulation and socio-emotional behavior, the book examines the growing body of evidence supporting the importance of the cerebellum in emotions, cognition, and psychopathology. Going on to discuss the implications of cerebellar abnormalities, Schutter analyzes groundbreaking research and explores how cerebellar abnormalities are associated with disruption in associative learning in anxiety, the pathophysiology of depression and cognitive regulation, the synchronization of information processing in schizophrenia, the aberrant connectivity patterns in autism spectrum disorders, and explosive forms of aggressive behavior.

Collating pioneering research on the multifaceted role of the cerebellum, this book will be essential reading for students and researchers of neurology and psychopathology.

Chapter 1

Evolution and basic anatomy
of the cerebellum

The cerebellum in evolution

Fossil records of the cranial capacity of our ancestors suggest that an initial slow increase in brain volumes early in hominin brain evolution was followed by a period of more rapid expansion over the last 2 million years (Reyes & Sherwood, 2015). Comparative anatomical studies indicate that the increase of human brain size was likely associated with the extension of the frontal, temporal and parietal association areas (Finlay & Darlington, 1995). Furthermore, it has been proposed that the expansion of the association areas was paralleled by a substantial increase in long-range white matter connectivity between these neo-cortical regions (Verendeev & Sherwoord, 2017). The ability of hominins to express behavioral flexibility in unpredictable environments, incorporate contextual information into adaptive decision making, and learn from experience across situations has been directly linked to the growth of the neo-cortical areas and its connections (Lefebvre, 2004). Especially, the large volumetric increase in gray as well as white matter of the prefrontal cortex is designated as being among the hallmarks of cortical brain evolution and behavioral repertoire of the human species as compared to non-human primates (Balsters et al., 2010). However, this view has been criticized as ‘cortico-centric myopia’ for neglecting the co-evolution of other interconnected subcortical brain regions (Parvizi, 2009). This view proposes that evolutionary changes in brain constitution and our mental capacities should be understood in terms of alterations in functional systems that involve interconnected regions. According to a line of comparative studies, the cerebral cortex supposedly evolved from two subcortical (limbic) brain structures: the amygdala and hippocampus (Sanides, 1964). This framework of mammalian brain evolution proposes that each structure contributed to two trajectories of cortical development (Giacco, 2006). The ventral system arguably originates from the amygdala and is involved in evaluating and assigning meaning (saliency) to stimuli, giving rise to motivational tendencies. This stream includes orbitofrontal and ventrolateral prefrontal cortex, insula and temporal lobe areas. The dorsal stream supposedly stems from the hippocampus and is specialized in representing the environment in space and time. The dorsal stream can be further subdivided into the dorsolateral and medial frontal cortex areas, supplementary motor area, and parietal lobe areas. These regions are involved in orchestrating goal-directed actions.

Based on the assumed functional differentiations between the ventral and dorsal cortical streams and their subcortical sources, the latter is more specialized in processing sensory-perceptual and cognitive regulation, whereas the former is dedicated to the processing of visceral and affective signals. The development of the cerebral cortex thus has its roots in the more ancient subcortical parts of the brain. This suggests that the cortical expansion represents a functional specialization of the older neural circuits, which in turn offers a neural foundation for extended mental abilities and a wide range of behavioral expressions. As we will see throughout this book, the structural neuro-anatomical architecture implies that our higher cortico-centered cognitive faculties are nested in the primordial limbic circuitries dedicated to motivation and emotion. Throughout evolution, the emergence of functional specialized brain circuits allowed animals to adapt to changing environmental demands and increase the likelihood of survival of the species.

It has been proposed that our brain consists of three phylogenetically distinct circuits (Maclean, 1990). According to the triune brain framework, the evolutionary oldest system is comprised of the brainstem-striatal complex that harbors the regulation of our vital bodily functions and primary forms of behavior (e.g., fight or flight) associated with survival and procreation. Subsequent (limbic) regions, including the thalamo-cingulate connections, are arguably evolved from the brainstem-striatal complex and associated with increasingly more complex patterns of (socio-emotional) behavior. These regions have been collectively termed the limbic system. (Note: the term limbic lobe has been subject to much discussion in academia.) This system is more developed in mammals as compared to reptiles and birds. Finally, the cerebral cortex and its connections with limbic and striatal regions is the seat of our higher mental (cognitive) capacities that endow humans with the ability to consciously reflect on emotions, intentions and actions, and learn and regulate behavior.

Most neuro-evolutionary accounts of higher mental functions in humans ascribe a large role to the frontal cortex and its reciprocal connections to the subcortical regions. Even though there is no scientific reason to doubt its correctness, it turns out to be part of the whole (hi)story.

As we will see in the second part of this chapter, several taxonomies have been described that provide standards for a functional and structural de-compartmentalization of the cerebellum. Referring to the afferent connectivity-based tripartite classification, a similar phylogenetic trajectory is applicable to the cerebellum. The cerebellum has evolved out of the vestibular nuclei and began as a small outgrowth of the brainstem. These first rudiments of a cerebellum appeared in pre-vertebrate jawless fish (e.g., lampreys) over 500 million years ago (mya). Cartilaginous fishes that lived 400 mya show a well-developed cerebellum that already exhibits the basic organizational properties found in the modern human cerebellum. The cerebellum, which is Latin for ‘little brain,’ owes its name to its resemblance to the big brain (cerebrum). Like the cerebrum, the cerebellum consists of two hemispheres with white matter fibers that project to and from the cerebellar cortex and subcortical (deep) nuclei.

In concordance with the topographic connectivity maps of the cerebellum that appear to parallel the phylogenetic discourse of the triune brain concept, the vestibulocerebellum is the most ancient part of the cerebellum and is known as the archicerebellum. Its afferent and efferent connections are exclusively with the lower regions of the central nervous system (i.e., brainstem and spinal cord). The paleocerebellum, the evolutionary nickname for the spinocerebellum, shows a wide range of connections to subcortical brain regions, of which many involve the limbic system. Documented observations of strong visceral and emotional responses to intracranial electric stimulation of the vermis in animals (Zanchetti & Zoccolini, 1954), as well as correlations between increased neural activity in the fastigial nucleus of the deep cerebellar nuclei (DCN) during fear and anger in humans (Heath et al., 1974) not only concur with the available neuroanatomical findings, but clearly demonstrate the need to seriously consider the cerebellum part of the ancestral affective circuits of the human brain (Anand et al., 1959). The medial part of the cerebellum is aptly called the ‘limbic’ cerebellum (Schmahmann, 2000).

The posterolateral hemispheres of the cerebellum or neocerebellum have developed relatively recently in human brain evolution. The cerebellar cortex projects to the dentate nucleus of the DCN, which in turn connects to the thalamo-cortical system. The seminal work by Peter Strick and colleagues has provided us with detailed anatomical maps of the dentate nucleus. Approximately 30 percent of the output channels in the dentate projects to the primary motor cortex, suggesting that the majority of output channels project to non-motor related cortical areas (Strick et al., 2009). For example, the output channels to the prefrontal cortex are found to cluster in the ventral regions of the dentate, whereas the output channels to the motor cortex are located more dorsally. Thus, connections to association areas of the cerebral cortex make the neocerebellum particularly apt to participate in neural processes associated with non-motor-related functions. In addition, the lateral part of the dentate is evolved more recently than the medial part and coincided with the expansion of the cerebellar hemispheres and the temporal and frontal cerebral cortical regions (Dow, 1942). These observations added to the notion that the cerebellum and cerebral cortex evolved in concert. Further evidence for the reciprocal evolution of the cerebellum and cerebral cortex has been provided using endocranial analyses (Weaver, 2005). Even though this kind of analyses faces several difficulties, such as finding reliable markings on the inside of the cranium, the cerebellum provides an exception, as it occupies the well delineated posterior cranial fossa (Weaver, 2005).

Modelling based on endocasts suggests that the evolution of the cerebellum and cerebral cortex of the human species is characterized by three phylogenetic stages (Weaver, 2005).

During the Pliocene and Early Pleistocene (~5.3 million–781,000 years ago), encephalization (i.e., increase brain–body ratio) was associated with volumetric expansion of the cerebral cortex and humans demonstrated technical advancements in foraging. It was not until the Middle to Late Pleistocene (~780,000–126,000 years ago) that extensive encephalization occurred that mainly involved enlargement of the cerebral cortex. The human species started to display increasing complex behavior that arguably involved substantial neocortical volumes. The Late Pleistocene (126,000–11,700 years ago) witnessed an increase in cerebellar capacity that may have further contributed to the socio-emotive and cognitive capacities of the human species (Weaver, 2005).

Researchers recently discovered that, among protein coding genes, there is no reason to assume that selection of genes is restricted or biased towards the development of the cerebral cortex exclusively (Harrison & Montgomery, 2017). In other words, protein-coding genes involved in the development of the cerebellum stand an equal chance of being selected as genes associated with cerebral cortical development. In fact, preliminary evidence indicates that protein-coding genes involved in cerebellum development may explain the accelerated rate of cerebellar volumes during the Late Pleistocene era (Harrison & Montgomery, 2017).

Moreover, a study that examined evolutionary rate changes along the branches of phylogenetic trees showed that the brains of humans and other apes in fact developed larger cerebella relative to neocortical volumes in comparison to other primates (Barton & Venditti, 2014). This can be taken as evidence to support the idea that the cerebellum is involved in complex functions that are thought to be mainly rooted in the neocortex.

While the neocortical expansion was dominated by relative larger increases in white (connections) to gray (neurons) matter (neurons), the opposite was happening to the cerebellum (Herculano-Houzel, 2010). As white matter evolved less rapidly in the cerebellum, the number of neurons in the cerebellum started to exceed the number of neurons in the neocortex by a 4:1 ratio (Herculano-Houzel, 2010). As such, the role of the cerebellum in molding the cerebello-cortical pathways in the evolutionary discourse may have been more important than previously thought (Whiting & Barton, 2003). Furthermore, the cortico-cerebellar system appears to be largely conserved throughout human evolution primary, favoring the view of the re-scaling of existing assemblies and its connections rather than the formation of new structures (Balsters et al., 2010).

As we will see in the second part of this chapter, the cerebellum has widespread topographical mappings unto other parts of the brain that seem to reflect the different neurophylogenic stages. Also, the cerebello-cortical connections are not random, but organized in a series of modular loops that show an isomorphic-like architecture (Ramnani, 2006). In agreement with Maclean’s evolutionary framework of functional brain organization, the cerebello-cortical loops between the posterior cerebellar hemispheres and the heteromodal cortical associat...

Table of contents

• Cover
• Half Title Page
• Title Page
• Copyright
• Dedication
• Contents
• Preface
• Foreword
• 1 Evolution and basic anatomy of the cerebellum
• 2 The cerebellum link to motivation and emotion
• 3 Disorders of fear and anxiety: a big role for the little brain?
• 4 The cerebellar basis of mood disorders
• 5 Cerebellum and affective dysmetria in schizophrenia
• 6 The socio-emotional cerebellum in autism spectrum disorder
• 7 Emotionally explosive minds: a cerebellum-oriented theory on reactive aggression
• 8 Epilogue
• Index