Scientific Understanding of Consciousness
Cerebellum and consciousness
Although the cerebellum has no direct role in consciousness, the results of prior cerebellum functionality is stored in neural circuits as procedural memories. These procedural memories of prior movements and activities then participate in the orientation function of the sense of self to contribute to the ‘remembered present’ yielding core consciousness.
Cerebellum is necessary for coordinating the specific repertoire of movements that are needed for well-executed, the skilled motion and for organizing the timing of these movements. (Squire & Kandel; Memory, 178)
The cerebellum receives real-time signals of body positions and motion and forms real-time neural signals that yield smooth coordinated body movements.
The cerebellum is one of the subcortical structures connected to the cortex via a set of parallel, unidirectional pathways. These pathways constitute one of the three topological networks of the brain.
Planning-tuning-motor output of the basal ganglia and cerebellum are input to the cortex via the thalamus. (Arbib - Handbook of Brain Theory and Neural Networks; Mumford; Thalamus, 981)
Research Study — Reward Expectation Encoded in Cerebellar Granule Cells
Cerebellum involved with Timing and Rhythm
Cerebellum has connections to many parts of the brain involved in attention and is intimately involved with the higher functions, setting the timing and rhythm and other aspects of language, memory, and emotion. (Ratey; User's Guide to Brain, 305)
Cerebellum a Most Sophisticated Signal Processing Structure
Cerebellum appears to be the most sophisticated signal processing structure of the brain. (Squire; Fundamental Neuroscience, 870)
Cerebellum regulates functions that are localized in other parts of the brain. (Squire; Fundamental Neuroscience, 870)
Through its many mossy fibers and granule cells, Purkinje cells are presented with an enormously diverse input that reflects the state of the body, the state of the environment, and the internal state of the brain. (Squire; Fundamental Neuroscience, 870)
Through the training influence of its climbing fibers, Purkinje cells learn to detect the occurrences of complex patterns of state, which mark the times at which they need to use their powerful inhibition to shape cerebellar output in order to regulate populations of neurons in other parts of the brain. (Squire; Fundamental Neuroscience, 870)
Nature Reviews Neuroscience 12, 327-344 (June 2011)
Spatiotemporal firing patterns in the cerebellum
Chris I. De Zeeuw, Freek E. Hoebeek, Laurens W. J. Bosman, Martijn Schonewille, Laurens Witter & Sebastiaan K. Koekkoek
Neurons are generally considered to communicate information by increasing or decreasing their firing rate. However, in principle, they could in addition convey messages by using specific spatiotemporal patterns of spiking activities and silent intervals. Here, we review expanding lines of evidence that such spatiotemporal coding occurs in the cerebellum, and that the olivocerebellar system is optimally designed to generate and employ precise patterns of complex spikes and simple spikes during the acquisition and consolidation of motor skills. These spatiotemporal patterns may complement rate coding, thus enabling precise control of motor and cognitive processing at a high spatiotemporal resolution by fine-tuning sensorimotor integration and coordination.
Cerebellum in Regulation of Highly Skilled Movements
All vertebrate animals have a cerebellum with highly preserved phylogenetic homology, and it continues to serve identical functions. (Buzsáki; Rhythms of the Brain, 363)
Cerebellum is concerned with the regulation of highly skilled movements, especially the planning and execution of complex spatial and temporal sequences of movement, including speech. (Purves; Neuroscience, 435)
Cerebellum might be involved in musical emotion. (Levitin; Your Brain on Music, 178)
The cerebellum is a system for adaptive feedforward motor control. (Rolls & Treves; Neural Networks, 189)
There is insufficient time during rapid movements for feedback control to operate, and the hypothesis is that the cerebellum performs feedforward control by learning to control the motor commands to the limbs and body in such a way that movements are smooth and precise. (Rolls & Treves; Neural Networks, 189)
Link to — Cerebellum multiple loops diagram — cerebellum is organized as multiple parallel loops without interloop communication.
Cerebellum heavily involved with FAPs
Cerebellum is important in earlier stages of motor skill learning. (Squire & Kandel; Memory, 178)
Purkinje cells of the cerebellum have long term depression of synaptic transmission (LTD), a form of synaptic plasticity that may underlie certain forms of motor learning. (Kandel; Principles of Neural Science, 240)
Cerebellum is necessary for coordinating the specific repertoire of movements that are needed for well-executed, skilled motion and for organizing the timing of these movements. (Squire & Kandel; Memory, 178)
Stroke victims with cerebellar damage struggle for the rest of their lives with simple physical maneuvers like walking up and down stairs. Instead of being able automatically to put their feet down in the right place on a stairstep, stroke victims with cerebellar damage have to consciously think about where to put their feet. (Ratey; User's Guide to Brain, 305)
Autistic patients and cerebellum stroke victims find it harder to shift their attention quickly from one thing to another. People with autism and those with cerebellum damage are slower to pick up on and react to new stimuli in the environment, making it harder for them to manage social interactions, which are characterized by constantly changing stimuli. Like putting our feet where we want them without having to think about it, our ability to put our attention where we want it without having to think about it is coordinated by the cerebellum. (Ratey; User's Guide to Brain, 305ff)
Loop between cortex and subcortical structures
The cerebral cortex is by far the largest source of inputs to the cerebellum. The majority originate in the primary motor and premotor cortices of the frontal lobe, the primary and secondary somatosensory cortices of the anterior parietal lobe, and the secondary visual regions of the posterior parietal lobe. (Purves; Neuroscience, 438)
Cerebellum projects to motor neurons in the cortex via a relay in the thalamus and in the brainstem. (Purves; Neuroscience, 440)
Thalamus a major relay station in the motor system
Ventral lateral nucleus of the thalamus, like the ventral anterior nucleus, is a major relay station in the motor system linking the cerebellum, basal ganglia, and the cerebral cortex. (Afifi; Functional Neuroanatomy, 245)
Ventral lateral nucleus of the thalamus links the cerebellum with the cerebral cortex. It belongs to the modality-specific and motor groups of thalamic nuclei. (Afifi; Functional Neuroanatomy, 245)
Cerebellum fibers project on the ventral lateral nucleus of the thalamus. Collaterals of the system project on intralaminar nuclei. (Afifi; Functional Neuroanatomy, 247)
Cerebella cortex receives two types of afferents: climbing fibers and mossy fibers, and generates a single output system, the axons of Purkinje cells. (Shepherd; Synaptic Organization of the Brain, 255)
Intrinsic excitability of the Purkinje cell and of the cerebellar nuclear cell membrane; the crystal-like organization of the synaptic connectivity of the cerebellar cortex. (Shepherd; Synaptic Organization of the Brain, 256)
Cerebellar peduncles connect cerebellum with rest of central nervous system
Cerebellum as a whole is connected to the rest of the central nervous system by three large fiber bundles, the cerebellar peduncles. (Shepherd; Synaptic Organization of the Brain, 255)
Cerebellum is enlarged in humans. One part of the cerebellum, the dentate nucleus in particular, is larger than expected. This area receives input neurons from the lateral cerebellar cortex and send output neurons to the cerebral cortex via the thalamus. The thalamus sorts and directs sensory information arriving from other parts of the nervous system. Growing evidence that the cerebellum contributes to cognitive as well as motor function. (Gazzaniga; Human, 22)
Control of movement is central to the nature of the mind
Cerebellum is evolutionarily the oldest part of the brain. (Levitin; Your Brain on Music, 83)
Cerebellum is involved in emotions and the planning of movements. (Levitin; Your Brain on Music, 83)
The cerebellum is essential in early motor learning that relates the categorization of gestures to perceptual categorizations. The cerebellum contributes to feature correlation and is an indispensable early component in forming the basis of memory and ultimately of primary consciousness; however, the cerebellum has no direct role in consciousness. (Edelman; Remembered Present, 126)
Cerebellum influences movements by modifying activity patterns of the upper motor neurons. (Purves; Neuroscience, 435)
Primary function of the cerebellum is to detect the difference, or motor error, between an intended movement and the actual movement, and through its projections to the upper motor neurons, to reduce the error. (Purves; Neuroscience, 435)
Cerebellum - overall organization and subdivisions - (diagram) (Purves; Neuroscience, 436)
Inferior Olive - (diagram) (Purves; Neuroscience, 438)
Cerebellum outputs to cerebral cortex - (diagram) (diagram) (Purves; Neuroscience, 440)
Most motor processing is handled by the cerebellum and its associated incoming and outgoing systems. (Llinás; I of the Vortex, 50)
The olivocerebellar system is the prime candidate for a neural assembly capable of optimizing and simplifying motor control. (Llinás; I of the Vortex, 50)
Probabilistic descriptions are not required for all neurons in the brain. For Purkinje cells in the cerebellum, for example, in which one neuron makes thousands of synapses on its target cell, statistical fluctuations in synaptic strength are very small. (Stevens; Cortical Theory, 242)
(paraphrase of Llinás, I of the Vortex, 44ff)
Several groups of central neurons (nuclei) such as the inferior olivary nucleus (IO) play a fundamental role in movement coordination. In the case of the IO neurons, their axons group to form nerve fiber bundles that route together into the cerebellum, which controls motor coordination. Fibers arising from the (IO) end by branching onto the main neurons of the cerebellar cortex Purkinje cells. These are the largest nerve cells in the brain, and the ends of the (IO) climbing-fiber axons, climb up over the Purkinje cells' branching dendrites, where neurons receive input from other neurons. Most movement control processing occurs in the cerebellum, and the climbing fibers powerful synaptic inputs in the vertebrate central nervous system, play an important role in motor control. Purkinje cells are inhibitory onto their target neurons. Damage to the IO or to the climbing fibers causes immediate, severe, and irreversible abolition of many aspects of motor coordination, both in the timing of movements and in the correct negotiation of movement through three-dimensional space: wrong timing, wrong placement. The IO plays such an important role in timing that animals with damage to this system have problems learning new motor behaviors. This does not mean that the cerebellum is the seat of motor learning, as some contemporary scientists believe.
IO Cell Oscillation, Cerebellum Drive Movement; Physiological Tremor
Intracellular recording from IO cells has demonstrated that the transmembrane voltage in these cells oscillates spontaneously (at 8-12 Hz). IO cells fire action potentials (spikes) at a frequency of 1-2 Hz (spikes per second), and although they do not fire on every oscillation, when they do, it occurs at the peak of the wave. It should be pointed out that this is not an isolated phenomenon, but that such IO activity is seen across many species.
IO cells fire their action potentials in a rhythmic fashion, and we also know a great deal about the intricate interplay of membrane conductances (ionic flow) that underlies the generation of this oscillatory activity. This rhythmic activity is sometimes referred to as regenerative firing, for such cells are capable of generating action potentials without the help of excitatory input converging on them.
Imagine that the pattern of electrical activity occurring simultaneously in many cells that sense each other electrically is imparted to the Purkinje cells of the cerebellar cortex by the climbing fibers and to cells in the cerebellar nuclei that can drive movement. If we remember that the cerebellum is the neuronal area where most of the control of movement coordination is processed, then we are getting closer, physiologically speaking, to our timing signal for the control of movement. Oscillation of the inferior olive results in a slight tremor that we all have at close to 10 Hz, even when we are not moving, This slight movement (known as physiological tremor) serves to time movements, like a metronome does when we are learning to play a musical instrument. Interestingly, no one can move faster than they can tremble. Indeed, one more echo of Bernstein's words is in order: "Is there no reason to suppose that this [tremor] frequency marks the appearance of rhythmic oscillations in the excitability of all, or of the main elements of the . . . motor apparatus, in which a mutual synchronization through rhythm is doubtless necessary?"
We have discussed physiological tremor and have surmised that it is a reflection at the musculoskeletal level of a central timing mechanism. The studies of IO anatomy and function are all consistent with the idea that the IO is in fact operating as a timing mechanism for the rhythmic orchestration of such premotor signals required for the genesis of coordinated movement. But the proof is in the pudding: we have chased tremor up into the brain, can we chase it back down again?
There is strong scientific evidence to indicate the relationship of the IO to tremor. An important question to ask is whether the IO is rhythmically active when a voluntary rhythmic movement is performed. We know that the initiation of a voluntary movement is highly associated with the phase of tremor. In one study, by use of multiple, simultaneous microelectrode recordings of Purkinje cell activity during pulsatile protrusions of the tongue in the free-moving, unanesthetized rat, a clear and robust pattern of activity of the IO was observed. Pulsate organization of movement may well be related to rhythmic, ensemble output of the IO.
(end of paraphrase)
Most motor processing is handled by the cerebellum and its associated incoming and outgoing systems. Motor control therefore must operate as a process whereby motor output is restricted (controlled) to an optimally small subset of all possible movements. This optimization/simplification process is discontinuous through time with pulse-like control of functional collectives of muscles, with synergies predisposed to work together for a desired movement sequence. This control, which is necessarily pulsatile, must operate often enough to minimize accelerative transients so that jerkiness in a movement is smoothed out. Finally, this control must be labile. It must be able to reconfigure itself readily, allowing for a nearly infinite ability to appropriate need-to-use-this-moment-only combinations and recombinations of muscle synergies. The ability of this control system to do so should mirror in time the transience of muscle configurations as they are recruited and discarded during a voluntary movement sequence. (Llinás, I of the Vortex, 50)
The olivocerebellar system neural assembly is capable of optimizing and simplifying motor control: it is temporally pulsatile and rapidly, dynamically self-reorganizing in the spatial domain.(Llinás, I of the Vortex, 50)
Link to — Consciousness Subject Outline
Further discussion — Covington Theory of Consciousness