In the pages of this site, we almost exclusively refer to the most common strokes, and until now, we have never discussed the topic of cerebellar stroke and what is the cerebellum. This is a particularly complex issue, on one hand due to the complexity of the functions that the cerebellum performs, on the other because it is a rarer injury compared to those caused to the cerebral hemispheres (approximately 2-3% of strokes).
Despite this, the treatment of the cerebellar patient is an issue that must be addressed, because the patient who survives an injury of this level, often presents problems that are quite incapacitating that limit him, sometimes even in the acts of minimal autonomy, also the mere fact of standing is impossible.
Only by studying in depth, the role of the cerebellum in relation to movement we can expect to be able to process the rehabilitation therapy that best suits the patient’s needs with cerebellar injury.
As we will see later in the course of this article, the cerebellum has undergone a long process of reinterpretation by researchers in the last century, and it is time to transfer this interpretive evolution to our operational field of physiotherapy, strictly reconsidering our work in the gym.
A common and widespread custom is to think of the cerebellum as a structure of our central nervous system, member of motor coordination and balance center. However, as we will learn throughout this article, in the last two decades, thanks to scientific studies, the cerebellum was also finally recognized by the scientific community as an “organ” that is capable of allowing us sophisticated cognitive functions, on which our motor behavior depends or not.
Treating the topic of rehabilitation after a stroke, the study of the cerebellum could not be kept out of our attention. For this reason, the objectives of this work will be:
- Analyze the evolution of its interpretation during the progress of scientific knowledge
- Study the cognitive and behavioral role of the cerebellum and the relations it interweaves with other brain structures
- Observe how the study of the cerebellum not only helps in the field of recovery from injuries of the cerebellum research, but also those of the brain, more widely discussed in our writings
- Use some working hypotheses based on the scientific evidence present in the literature.
Evolution of the cerebellum role interpretation
When speaking of the evolution of the history of the interpretation of the functions attributed to the cerebellum, it is impossible not highlight Sir Gordon Morgan Holmes who participated as a neurologist advisor in the military camps of the First World War. The confrontations obviously guaranteed Holmes, a great observer, a remarkable experience, in which he bases his pioneering studies on the visual cortex and cerebellum.
These two regions of interest were not random; in fact, they played a fundamental role in some insignificant circumstances.
The first was that at the time, the bullets were smaller and less deformable on impact with the skull, determining a smaller shock wave and then a reduced penetration wound; this guaranteed more survival chances for soldiers even if they were fired at battle.
The second was given by the shape of the helmet supplied to the British Army, the Brodie, which exposed the rear and lower part of the skull to bullet blows, corresponding to the area of the cerebellum and occipital lobes of the brain.
For decades, neurology enjoyed Sir Holmes’ acute observations, both for the study of the symptoms of cerebellar injury, and for the hypothesis of the functioning of such a structure. Consider the fact that only 3% of strokes are in charge of the cerebellum, and the death rate from this type of injury is very high, both due to the extreme contiguity with the midbrain structures that regulate vital functions and to possible hydrocephalus to obstruction of the cerebrospinal fluid.
Holmes’ careful, accurate, and pioneering studies of cerebellar functions focused on motor effects:
[…From this analysis of the symptoms caused by lesions of the cerebellum in humans, it is evident that the essential problems are:
- Postural hypotonia and the deterioration of some reactions of the hypotonic muscles
- Mild degrees of muscle weakness and fatigue
- Abnormalities in the rhythm, regularity, and strength of voluntary movements
- Alteration of some associated movements …] (Holmes 1939)
It is evident that, despite the accuracy of Sir Gordon Holmes’ effective observations, it was the year 1900 and although the statistical base on which the researcher could count was long, he did not have today´s technological tools, such as neuroimaging equipment, and the effects on cerebellar injuries were identified at a purely executive and motor level.
However, even in Holmes’s writings, observations regarding some cognitive disorders of his patients were not necessary and in the following decades to follow inverse analyzes, then at the autopsy of people with psychiatric disorders (dementia, Alzheimer’s disease, schizophrenia and autism) abnormalities of the cerebellum were revealed.
Change of direction
In the scientific literature, the works of Jeremy Schmamann from the 1990s represent a point of reference for a reinterpretation of the cerebellum on the cognitive basis of a trend change that has allowed the development of numerous scientific confirmations in the following years to the present day.
Schmamann, director of Ataxia at Massachusetts General Hospital, in his outstanding 1991 research “An emergent concept: cerebellar to higher functions” said:
[… More recently, however, neuroimaging and clinical studies have suggested once again that cerebellar abnormalities may be more than epiphenomena in patients with impaired intellectual or emotional capacity… It is recommended that patients with cerebellum lesions are studied from a neurobehavioral point of view] (Schmahmann 1991).
Obviously, in our field of rehabilitation, such neurophysiological reconsiderations must have repercussions in terms of re-adaptation of the physiotherapy so far proposed and based on the knowledge already reinterpreted.
[… Currently, the attribution of the cerebellum by many physiologists of definable “cognitive” functions and the contemporary refinement of a rehabilitation theory that proposes the reference in the study of recovery to processes related to consciousness, make an interesting reconsideration of cerebellar disease also from the perspective of the recovery pathophysiology…] (Carlo Perfetti 1998).
The phylogenetic evolution of the cerebellum and the evolution of its interpretation
To understand the evolution of the cerebellum role interpretation in humans, it is also interesting to consider the contribution of studies related to the development that this nervous structure has undergone during the evolution of our species. Studying how nature is investing in our central nervous system by making certain evolutionary choices instead of others, and it offers us an interesting perspective to better study the role of the cerebellum.
Despite the fact that the cerebellum contains four times the number of neurons in the cerebral cortex, the latter is sometimes identified as the crown of evolution and the biological substrate of the mental capacity of the human species. Robert A. Barton professor of Evolutionary Anthropology at Durham University in England, claims that evolutionary pressure has preferred to be directed at the cerebellum development, attributing such a trend to the functions of the cerebellum with respect to technical and social intelligence.
Narender Ramnani, a researcher at the Royal Holloway University in London, in his 2012 study concluded that a narrow view of the cerebellum role in motor control is inconsistent in light of new information on the cerebellum connections involving, not just the primary motor cortex, but also the prefrontal cortex and the posterior parietal cortex. Along with these structures, the cerebellum, according to Ramnani, plays a fundamental role in regulating the activities of the association cortex.
This system also seems to come from a co-evolutionary path. We will see later the importance of this connection between the cerebellum and the rest of the brain for behavioral purposes. For now, the significant fact is that the cerebellum fulfills its tasks in harmony with its roles played by other brain structures that are involved in cognitive functions, such as those linked to the perception and planning of actions and not only to the motor act itself. In short, these recent studies on the cerebellum evolution and its intimate connections with the cerebral apparatuses, which coincide with the functions related to decision making, prognosis, information analysis and motor organization, help us to finally “compensate” for the cerebellum entrusting it with a highly sophisticated cognitive role. (Riassunto dell’articolo di Ramani).
Cerebellum and Sensory tasks
James Mason Bower, an American neuroscientist, studied the cerebellum physiology in 1997, showing its fascinating role in motor organization and sensory acquisition in along with other cortical structures. Defining the cerebellum:
[… it is not responsible for itself or any behavioral function, whether it be “motor”, “sensory”, “cognitive”, but rather helps the efficiency of other brain structures which carry it out …]
To give a practical example of the relation between the cerebellum and the brain, imagine forming an orchestra of experienced musicians. Even if the conductor does not guide them, they will be able to complete the symphony demand, however, the conductor, in this case the cerebellum, will be able to make each professional render 100% of their talent, giving the piece greater harmony and majesty.
There is a study, which is very important to me, it is from Bower and I think that summarizing it here can help us understand the role of the cerebellum, remembering us the reason why we are entering the field of neurophysiology, allowing us a better interpretation of the necessary rehabilitation after a cerebellar stroke.
I imagine that at this point, in light of what was mentioned before, physiotherapy exercises where the patient is subjected to walking with the weights on the ankle to aid in gravitational management or offer muscle strengthening exercises may be incompatible from the neurophysiological perspective.
Bower noticed a first curious fact in rats that surprised him from the beginning. The tactile representations are present in the cerebellum and, therefore, receive the fibers of the body surface, and did not come from the lower joints as it was expected according to a “motor” and “postural” view of the cerebellum, but from the muzzle areas and partly by the front legs. These representation areas also had a mosaic conformation where each part fits with another, but not in the body since they were not anatomically adjacent “fractured somatotopy”, however, the disposition of this body “map” suggested that each part was connected with another, not from the anatomical but a functional point of view.
In fact, these areas were activated during tactile exploration and not during other stereotypical movements such as chewing. A similar representation to the rat has been identified in the cerebellum of mammals, for example, cats and primates, the latter were more evident in the representations of the forelimbs involved in tactile recognition tasks.
However, despite these observations, various authors interpreted this type of mosaic representation of body receptors surfaces, for the purposes of motor control. In fact, it is not easy to distinguish whether sensory acquisition is available to movement or, vice versa, it is movement to be available to sensory acquisition.
It seems almost a paradox style, if the chicken or the egg came first it actually represents a fundamental topic.
To solve this dilemma, we are going to use a study by Jia hong Gao, Co-Director of the Brain Research Imaging Center of the University of Chicago, whose study name already provides the answer:
“The brain is involved in the acquisition and discrimination of sensory data rather than motor control”
Through this study, the author wanted to verify the degree of activation of the dentate nucleus of the cerebellum according to the tasks that had more or less a sense of perception for the study subjects.
In a first task, the subjects were passed an abrasive paper under the tips of their hands without any request in either motor or discriminatory terms, then they were asked to recognize the surface proposed. Afterwards they were asked to grab and drop some objects on the floor and in the last task they were requested to grab an object and recognize if it was the same object or not in the other hand.
I summarize the results in this table, even if you already imagine in which activity the cerebellum saw a greater activation, I also emphasize the fact that in all the tasks required by Gao the individuals had their eyes closed. In this context I am happy to think that Prof. Carlo Perfetti, 30 years before this research, sensed the need to offer closed eye recognition exercises to patients with brain injuries, especially the tactile recognition exercise of perceiving different surfaces with their fingers was one of the first exercises of what is commonly known as the Perfetti method.
This is the result of various activations.
As expected, the increased activation of the cerebellum was when the task involved not only movement, but when, in addition to movement, the subject needed to know the object. The right dentate nucleus appeared more active than the left one; the authors have speculated that this difference, even if minimal, is attributed to the left cerebral hemisphere dominance of ambidextrous participants.
This contribution by Gao, besides clarifying the role of the cerebellum with respect to the acquisition of sensory data in order to build movement, makes us reflect on the rehabilitation practices that patients with cerebellar injuries are often forced to do, because they are still linked to the interpretation before the cerebellum, where the injury was the origin of hypotonia.
It is evident that if the interpretation of the sequele of a cerebellar lesion is directed to the reduction of muscle tone, it is immediately thought that exercise should be its reinforcement method. However, in light of these important studies where we realize that the cerebellum, besides reducing tone after its injury, also implies an alteration in the ability to capture information from the environment for proper motor organization:
“Isn’t it at least reasonable to think that exercise should contain at least one problem?” And that “Such a problem should, not only be a motor one, but also a cognitive and perceptual one?” One of the objectives of this article is not to define what should be done word by word against a cerebellar disease, I would not have the tools, but towards the end we will make operational assumptions regarding the exercises. At least plant a reasonable doubt about the muscular and neuromotor practices that do not consider the neurocognitive aspects that allow us to enter into a relationship with the world in need of severe and responsible consideration. In the Gao study just mentioned, it is useful to associate the work of Seong-Gi Kim, a researcher at the University of Pittsburg.
“Activation of a cerebellar output nucleus during cognitive processing”
The author shows that the cerebellum was not activated based on the motor complexity of the gesture, but on the complexity of the problem to be treated.
The investigator primarily asked the group of study subjects to perform two tasks while examining the degree of cerebellar activation.
In the first task that they had to move the colored pins from a tablet with holes to another without following a pattern, in the second task the movement of the pins from one base to the other had to satisfy some of the disposition rules. Also, in this case the maximum activation intensity was achieved in the task in which the subject was subjected to a problematic requirement from a cognitive point of view, a task in which the individual had to follow some rules, despite the motor fragmentation outside. The same in both tasks.
This study makes us reflect on the importance of offering our patients the problems that must be solved with the body and with use of perception. The study carried out by Kim, together with that one from Gao, helped us to clear the doubt that arose during Bower’s observations, that is, whether it was the movement to be at the service of perception or sensory acquisition was the parameter on which the motor organization.
Bower continues his research wondering why the mosaic representation that is present in the cerebellum of the body touch surfaces are not organized in a somatotopic way, but arranged according to a functional meaning, the cerebellum would act as an “integrator” of information from different regions of the body in charge of the same task.
This assumption leads us to associate what happens in the movement of the patient who has suffered a cerebellar stroke, meaning that it is a movement that is deficient from the point of view of the number of joints involved in the movement.
For example, during a task of grasping an object, where the patient usually first relaxes the whole arm and then moves the shoulder to reach the object with the pulse invariably extended avoiding to prevent fragmentation of the elbow-back-wrist and fingers in such a synchronized and contemporary organization, perhaps due to the difficulty found by the cerebellum in integrating and taking advantage of the information coming from the different joints.
The same reduction phenomenon of the joints brought into play during movement could be observed in the management of the trunk of the cerebellar patient. Whether sitting or standing in a right position and involved in walking, where the behavior of the spine seems very rigid and little fragmented, as if wishing to reduce the complex articulation of the spine (just think of the fact that the spine has 33 vertebrae to manage …).
According to the same author, the integrated information of perception of the cerebellum would serve to inform the so-called cerebral cortex to an organization of the exploration surfaces of our body, in order to facilitate a more accurate construction of information with the environment. Cerebellum activation during sensory data acquisition tasks is confirmed by another interesting study by Harry Jenkins. It detects greater activation of the cerebellum when the task under examination is a new task and not a learned one, than for example a task such as writing in a keyboard, while it gradually decreased as the task was learned by the subjects, despite the motor sequences being the same. This study not only confirms the role of the cerebellum during sensory data acquisition, but also highlights another important aspect for those dealing with post-stroke recovery, meaning that the cerebellum is involved in learning processes.
When I explain the role of the cerebellum during learning to my patients, I often make the example of driving a car, the first days we were learning to drive; we even took our hand off the wheel with difficulty to achieve the speed change. Today, after from several years of experience, we can drive, talk on the phone (wrong thing!), change the radio station and if we are in a chaotic city like Rome they can also use one hand to say “Hi!” to another driver and perhaps get to our home door without even remembering what we did: almost everything automatically.
From the first day we get in the car until when we internalize and make the handling automatic, our cerebellum did all the fireworks in terms of activation.
This will make us reflect on ways to propose the exercises: If it usually aims to the acquisition of a certain performance or by favoring the cerebellum in an innovative way. It will not be a simple debate where a healthy balance is likely to win between the two options, both for brain injured patients and for cerebellar injury patients.
To understand more fully, how to organize therapeutic activities aimed at the cerebellar patient, we must go further into the role of the cerebellum in order to behave and know the functions in which it participates. One of the cognitive processes, which the cerebellum provides its functions for, is the motor image, “…The motor image can be defined as a dynamic state in which the individual mentally simulates a certain action. This type of experience implies that the subject feels he is performing the action…” (Decety 1996).
Decety presents the same in his study
The cerebellum participates in mental activity: Tomographic measurements of regional cerebral blood flow, in light of studies on the cerebellum physiology, not considering its skills in motor image processing could mean missing the opportunity to be able to activate the cerebellum in a more complete and functional way for recovery.
It demonstrated that during motor imaging tasks, an activation of the cerebellum occurs, suggesting an active role for the cerebellum in movement programming, and then motor learning. We have discussed the topic of motor imaging extensively in this article, which I suggest you read to get a broader view of the topic. It is an evident fact that the brain contributes to action through provisional functions and that it participates in the creation of mental representation, crucial for the motor learning of new or complex actions, should stimulate the rehabilitator to consider the motor image as a tool for the recovery of the patient with cerebellar injury.
Diaschisis and the cerebellum
One of the objectives of this article is also to stimulate you to consider the functional implications of the cerebellum, despite the fact that we exclusively address the treatment of patients with hemiplegic brain injury and not necessarily a cerebellar one. In the previous sections, we have seen how much the functions of the cerebellum are intimately connected with the cerebral cortex functions; do you remember the example of the conductor?
As the action becomes the emergent property of a complex organization of our nervous system, we must take into consideration the recovery of the entire functional system, involving all its parts and the relation between them in an integrated way. For this reason despite the fact that we are facing the recovery of a patient with brain injury, it is reasonable also to consider, in our rehabilitation work, the functional implications that the cerebellum provides movement.
Another aspect of fundamental importance, which pushes us once again to take into consideration the cerebellum role in our rehabilitation practice also applied in patients who have not undergone a cerebellar injury, is provided by diaschisis.
The concept of diaschisis was first introduced by Von Monakov in 1914 and supported to this day by countless studies. By diaschisis, we refer to a remote deactivation of some nerve structures because of brain damage, such structures can undergo deactivation even if they are distanced from the injury. This is a topic of great importance for those involved in the rehabilitation of patients after a stroke, therefore, we will speak profoundly and more specifically in other articles.
The concept of diaschisis is mentioned in this article dedicated to the cerebellum, because one of the nerve structures most affected by this phenomenon is precisely the cerebellum.
Therefore, if we face a post-stroke recovery, after a brain injury that does not directly involve the cerebellum, we must have in mind that although the cerebellum was not anatomically affected, it suffers functional deterioration.
The functional alteration suffered seems to be related to the contribution made according to the injured area and not a tout court deactivation.
This fact leads us to suppose that the alterations the patient shows after a hemispheric injury, may not be simply the result of the real and direct biological damage of the nervous areas affected by ischemia, hemorrhage or trauma, but instead it may be the a result of direct damage added to the collateral damage of neuronal depression of nerve structures located at a distance from the injury, but with which a functional role is shared.
To simplify, we could hypothesize that for the recovery of the hemiplegic patient it may be important to proceed through rehabilitation, also taking into consideration the exercises that address the task of reactivating the cerebellum inhibited by diaschisis. Our exercises should consider the functional role of the cerebellum in relation to the brain areas directly affected by the injury, as we have seen previously: information management, motor problem resolution, motor image elaboration and the learning of new motor sequences.
Rehabilitation of the patient after cerebellar stroke
As it is described in the introduction, the cerebellum has an anatomical and highly complex organization, and also it is one of the objectives chosen by our evolutionary development, so we can imagine that any injury at any level of the cerebellum entails differences that should affect the daily routine of rehabilitation. Therefore, the following will be just generic working hypotheses regarding physiotherapeutic treatment of the cerebellar patient and these should only serve for the purpose of reflection and be subjected to test exercises. Most of these rehabilitation implications were already formulated in the 90s, by the Italian scholar Prof. Carlo Perfetti, in the cited text: Cerebellum and cognitive processes.
The presence of a problem in the exercise
As we were able to appreciate, thanks to the study carried out by Kim et al, the cerebellum is activated with motor tasks that have complexity from a cognitive point of view, and not just kinematics. Despite how many decades it was analyzed towards the results of cerebellar injury, as the main problem was considered the muscle disease that leads to hypotonia.
Therefore, it might be reasonable to reconsider physiotherapy activities that induce the cerebellar patient to muscle reinforcement, made from routine and repetitive tasks, because although they may have an effect on muscle volume and strength, they may not affect recovery from muscle quality movement. While preferential exercises could be the ones where the patient works on the resolution of a motor problem that has a cognitive meaning, that is, action planning, use of attention and the use of perception are involved.
Presence of sensory recognition and discrimination
Bower’s fascinating study of the cerebellum involvement in motor organization thanks to its function of integrating information built through the surfaces of our body’s receptors, leads us to think that therapeutic exercise must be able to contain, within the problem proposed to the patient, a sensory recognition task in order to bring into play the cerebellum role as a regulator of movements on the bases of information built with the environment. An often “savvy” defined exercise.
Presence of movement
Unlike the hemiplegic patient, who presents a specific motor composed of elemental components of movement known as spasticity, the patient with cerebellar injury presents a different specifically motor one, where motor possibilities often remain intact but disorganized. Also, in light of Gao’s studies where we observed the cerebellum activate on a massive scale during a recognition task through the movement produced by the patient with reference to the activation evidenced by a tactile discrimination task of the movement produced by the operator. We can consider the hypothesis, which affirms that the exercise could contain the intentional movement produced by the patient and less induced by the operator. For example, as a result of the distinction that is commonly used in neurocognitive rehabilitation according to Perfetti, exercises in 2nd and 3rd grade are preferred compared to 1st grade exercises, where the patient allows himself to be guided during movement and where he calls the attention to the control of elemental components of spasticity.
Multisegmental and multisensory proposal
In Bower’s study, the deductions about the arrangement and conformation meaning of the cerebellum representations of the exploration of our body surfaces, always make us reflect on the possibility of stimulating the cerebellum by proposing cognitive problems to our patient and where movement has a value, but allowing it to perform its function of integrating information between the different segments of our body. Thus putting the patient in the position of having to relate the information simultaneously constructed with multiple parts of the body within an action and not simply use a single joint.
The same “fractured” mosaic representation, and the type of activation of the nerve fibers connected to them, as the author speculates, could make sense for integrating different information modalities within the surfaces of individual receptors. Therefore, it could be a hypothesis to formulate an exercise whose solution can be found through the integration of the different fields of information.
This, at the hypothetical level, could be one of the reasons why, through empirical observations, it was detected that patients with cerebellum lesions often present perception problems especially in weight recognition tasks. Weight is, in fact, complex information resulting from the integration of other information areas, we recognize the weight of an object or put together our body parameters such as movement (synesthetic information), touch (haptic information), pressure and sense of effort (the latter has not yet been studied very well)
[… The neural bases of the sensation of exertion have not yet been discovered. It seems that the brain uses the motor command itself to measure tension …] (Alain Benthoz (Berthoz) “Les sens du mouvement”)
As we have already anticipated gradually in the studies that demonstrated the activation of the cerebellum during motor learning tasks through the use of motor imagery, which could be a rehabilitation implication, to employ the use of movement forecasting in cognitive exercise, motor image so to speak.
Nevertheless, for those who deal with neurocognitive rehabilitation, they already do so in daily rehabilitation practice.
The importance of repetition to learn certain motor skills is indisputable, it is also true that patients with cerebellar injury have not lost certain motor skills, but their ability to organize movement in a harmonious and effective way has been altered. Therefore, it could be a working hypothesis based on leaving a space within our therapeutic approach to bring more and new cognitive exercises, where the patient can activate the cerebellum according to its already observed functions of “problem solver” in which the patient faces the need to analyze the procedures and rules of a new task solution every time.
Having observed the fact that the activation of the cerebellum decreases in relation to the acquisition and automation of the task, we find this working hypothesis interesting, in which new tasks are constantly proposed to the patient, although not so different from those already proposed for the recovery of certain functions, but with innovative features that force the patient to develop a new solution process.
I test this hypothesis in my daily practice, even with patients with brain and non-cerebellar lesions, taking into consideration studies on diaschisis, where even in the presence of a brain lesion, a reactivation of the cerebellum involved in the distance from the lesion in a neuronal depression becomes necessary.
Therefore, in daily physiotherapy sessions I leave a free space for at least one exercise a day that has these “cerebellar” characteristics, I define them as cerebellar exercises.
The role of the view and lobby
It is a very interesting topic, as the cerebellum integrates visual-spatial, proprioceptive and vestibular information, for this reason the topic will be explored with research and analysis of specific scientific contributions for us, and then continue to speculate on the rehabilitation implications. In a future article, we will discuss the topic of a possible therapeutic intervention for the recovery of integrative functions, including visual-spatial and vestibular information, together with an analysis of the concept of Cerebellar Ataxia.