week 9 Flashcards
(27 cards)
What are the gross divisions of the cerebellum?
The cerebellum is divided into three main regions: the lateral hemisphere (cerebrocerebellum), the intermediate or paravermal zone, and the vermis (spinocerebellum).
How does the “flattening of the cortical sheet” relate to cerebellar structure?
The cerebellar cortex is highly folded; its total length scales with body mass, while its width may be related to cognitive properties.
What are the approximate cell numbers in the human cerebellum?
The human cerebellum contains roughly 102 billion cells in total, including about 101 billion granule cells, 15–30 million Purkinje cells, around 150–200 million interneurons (Golgi, basket, stellate cells), and approximately 5 million nuclear cells.
What are the main layers of the cerebellar cortex and their functions?
The cerebellar cortex comprises the molecular layer (where parallel fibers run), the Purkinje cell layer (home to the sole output neurons of the cortex), and the granular layer (packed with granule cells that give rise to the parallel fibers).
What are the principal inputs to a Purkinje cell?
Each Purkinje cell receives roughly 200,000 excitatory inputs from parallel fibers (originating from granule cells) and one powerful climbing fiber input from the inferior olive.
How does the parallel-fibre/Purkinje cell (Marr-Albus) model of learning work?
This model explains that when parallel fibers and climbing fibers are simultaneously active, long-term depression (LTD) occurs at their synapses on Purkinje cells. This plastic change reduces Purkinje cell inhibition of the cerebellar nuclei, thereby fine-tuning motor commands and enabling learning from errors.
What role does LTD play in motor learning within the cerebellum?
LTD at the parallel fiber–Purkinje cell synapse decreases the inhibition imposed by Purkinje cells on the cerebellar nuclei, effectively disinhibiting downstream motor pathways so that errors in movement can be corrected and refined over time.
What is the role of the cerebellum in motor control?
The cerebellum coordinates fine motor control and skilled movement by integrating sensory inputs with motor commands, predicting the sensory consequences of actions, and rapidly adjusting ongoing movements.
How does the cerebellum utilize prediction in motor control?
It creates an internal model using an efference copy of motor commands to predict expected sensory feedback. By comparing this prediction with actual feedback, the cerebellum quickly corrects errors without waiting for slower sensory updates.
How does the Vestibulo-Ocular Reflex (VOR) exemplify cerebellar learning?
The VOR stabilizes vision during head movement by generating compensatory eye movements. Retinal slip (the error signal) drives climbing fiber activity, which induces LTD at Purkinje cells to adjust the reflex’s gain.
What is the mechanism underlying eye blink conditioning in the cerebellum?
In eye blink conditioning, a neutral stimulus (tone or light) activates parallel fibers while an air puff (unconditioned stimulus) activates climbing fibers. Their simultaneous activity triggers LTD at the Purkinje cell synapses, gradually establishing the conditioned blink response.
What is visuo-motor recalibration, and how does the cerebellum contribute to it?
Visuo-motor recalibration refers to the process by which the motor system adjusts to distorted visual inputs (for example, when wearing prism glasses). The cerebellum corrects errors by updating motor commands based on discrepancies between predicted and actual sensory feedback; lesions here block this adaptive learning.
What challenge is associated with studying skill learning and LTD in behaving animals?
Although LTD is assumed to underlie skill learning, it is difficult to measure directly in intact, behaving animals. Researchers often rely on recording complex spikes as an indirect index of cerebellar plasticity.
What are the principal output pathways of the cerebellum?
The cerebellum sends outputs from its deep nuclei (dentate, interposed, and fastigial) to the motor and premotor cortices via the thalamus, as well as to the brainstem and spinal cord (e.g., through the red nucleus).
What motor deficits can result from cerebellar damage?
Cerebellar lesions can lead to hypermetria (overshooting targets), intention tremor during movement, ataxia (loss of coordination), nystagmus, impaired balance, gait and speech disturbances, and in some cases, affective disorders impacting executive, emotional, and personality functions.
How might the cerebellum be involved in cognitive functions beyond motor control?
Given its extensive reciprocal connections with the prefrontal cortex and other areas, the cerebellum is thought to contribute to prediction and timing in cognitive domains such as language, working memory, and arithmetic, although these roles are still being explored and confirmed.
What are the current findings and challenges regarding cerebellar non-invasive brain stimulation (e.g., tDCS) and prediction?
Some studies have reported that transcranial direct current stimulation (tDCS) of the cerebellum can enhance prediction and cognitive performance. However, these effects are variable and difficult to consistently replicate, highlighting ongoing challenges in this line of research.
Which study provided quantitative insights into cerebellar anatomy across species?
The study by Sultan & Braitenberg (1993) examined the shapes and sizes of different mammalian cerebella, demonstrating how the length of the cerebellar cortical sheet correlates with body mass and suggesting that its width may reflect cognitive properties.
How is motor control organized hierarchically with respect to the cerebellum and basal ganglia?
Motor control follows a hierarchical structure where the basal ganglia are involved in planning, programming, and integration of motor commands. The motor cortex and pre-motor areas execute these commands, while the cerebellum provides fine-tuning through prediction and error correction, ensuring smooth and coordinated movement.
What are the distinct functional zones within the cerebellum as identified by resting state functional connectivity?
Resting state studies have delineated distinct, yet overlapping, zones in the cerebellum—namely the lateral hemisphere (cerebro-cerebellum), the intermediate or paravermal zone, and the vermis (spinocerebellum). These zones align with different aspects of motor and possibly cognitive functions.
What is the significance of the cerebellar deep nuclei in motor output?
The deep nuclei—dentate, interposed, and fastigial—serve as the main output channels of the cerebellum. They integrate the processed signals from the Purkinje cells and relay the information via the thalamus to motor and premotor cortices, as well as directly to brainstem centers and the spinal cord, thereby modulating movement.
How does the cerebellum contribute to eye-hand coordination?
By predicting the sensory outcomes of motor commands, the cerebellum helps match visual inputs with appropriate motor actions. This predictive mechanism is critical to ensuring smooth, well-timed coordination between the eyes and the hands during complex tasks.
Why is predictive control essential for fast and accurate movements?
Predictive control allows the brain to anticipate the outcome of motor actions. This means corrections can occur almost instantaneously—without waiting for slower sensory feedback—which is vital for fast, precise movements and tasks performed in environments with poor or delayed sensory input.
What have non-invasive brain stimulation studies revealed about cerebellar function in cognitive prediction?
Techniques such as transcranial direct current stimulation (tDCS) of the cerebellum have shown that modulating cerebellar activity can influence predictive aspects of cognition (e.g., language prediction and working memory). However, the results are variable and difficult to replicate consistently, underscoring the complexity of these networks.
