Sunday, December 30, 2007

Supervised Motor Learning in the Cerebellum

Recap

In the previous article, I made a falsifiable prediction about the cerebellum based on my interpretation of certain metaphorical passages in the book of Revelation. One should note that the current consensus among neurologists regarding cerebellar contribution to speech processing in the brain goes contrary to my prediction. So clearly, nobody can accuse me of using existing scientific literature to make predictions after the fact. Many neurologists have concluded that the cerebellum participates in the production of speech after noticing that patients with cerebellar lesions exhibit speech difficulties. My claim is that they are mistaken and that the cerebellum contributes nothing at all to the generation of speech and language. Its purpose is to attend to routine non-speech-related motor tasks (such as maintaining posture) that would otherwise have to be performed by the motor cortex. I argue that the type of speech impairment observed in patients with cerebellar lesions is due to the motor cortex having to attend to tasks that should normally be handled by the cerebellum. This results in frequent interruptions that manifest themselves as disjointed speech.

One More Cerebellar Prediction From the Bible

The cerebellum is a sensorimotor learning system. Although its learning principles are simple, it can be trained to perform sophisticated sensorimotor tasks such as maintaining posture, walking, running, self-balancing, navigating, etc… Its actions are purely reactive, that is to say, it cannot anticipate the outcomes of sensory or motor patterns. In other words, the cerebellum uses sensory signals to directly control motor effectors in real time.

Two main types of sensory signals are used in the brain. The first is a transient spike or a short spike burst that marks the onset or offset of a sensory phenomenon. The second is a sustained spike train that lasts for the duration of the sensed phenomenon. In the neurobiological literature, these two types of signals arriving at the cortex from the retina are known to go through the magnocellular and the parvocellular pathways. Based on my understanding of the metaphors of Smyrna and Laodicea in the book of Revelation, I can confidently predict that the cerebellum (Laodicea) processes only the second type (sustained spike train) of signals. The Bible uses two metaphors to distinguish between the two: rich (sustained) and poor (transient).

Supervised Learning

In my opinion, the training principle used in the cerebellum is rather simple. It is a trial and error process. Essentially, parallel fibers that receive sensory signals from various places in the body make random synaptic connections with a huge number of Purkinje cells. The output signals generated by a Purkinje cell ultimately activate a muscle. As long as the Purkinje cell is receiving input signals from the parallel fibers, the muscle remains activated. During training, a mature behavior group in the motor cortex (symbolized by the church of Philadelphia) monitors the activation of the muscles under its control and sends a stop signal whenever a muscle is activated longer than it should be. When the stop signal reaches the climbing fiber on the Purkinje cell, a powerful corrective spike is generated. This, in turn, greatly weakens the connections with any parallel fiber that is still firing. Eventually, only the parallel fibers that activate the Purkinje cells at the right time retain their synaptic connections.

Robotic Cerebellum

I think that a simulated software cerebellum can serve as a very effective motor learning system for a humanoid robot. A human trainer using a special sensor-equipped suit that mimics the shape and limbs of the actual robot could teach such a robot to perform various complex tasks such as waking, climbing stairs, etc... Just a thought.

Thursday, December 13, 2007

Falsifiable Prediction About Human Cerebellum From the Bible

Note: What follows was copied from the previous article. I felt that it should be separate.

According to my interpretation of the Biblical texts, the cerebellum is a supervised automaton. It is trained by the motor cortex to take over certain routine motor tasks whenever the basal ganglia and motor cortex are busy reasoning internally or engaging in some other motor activity. My understanding of the metaphorical messages to the church of Pergamum (Broca's area) and Laodicea (cerebellum) in the book of Revelation is that speech is always an attentional or volitional (as opposed to automatic or unconscious) process that involves corrective feedback from the basal ganglia. The cerebellum is not directly involved in processing speech and language. The indication is that the cerebellum can have motor control over the entire body except the mouth, throat and tongue muscles. This means that activities like eating, chewing and swallowing are also excluded from cerebellar control.

How can this prediction be falsified? In my opinion, it suffices to examine the brain pathways that link the motor cortex with the cerebellum. The prediction is that there are no pathways between the cerebellum and any parts of the motor cortex that controls the mouth, speech, etc… Another way to falsify this prediction would be to compare MRI images of cerebellar activities when a subject is speaking (in a relaxed position) and engaging in non-speech related activities. I predict that the data will support the claim that the cerebellum does not generate speech.

Another interesting consequence to this prediction is that serious damage to the cerebellum should be accompanied by a loss of speech capability while the subject is engaged in other motor activities (e.g., walking). The reason is that the subject can no longer rely on the cerebellum for routine tasks (while speaking) and must consciously attend to them. We can only attend to one conscious task at a time. This is why the cerebellum is so important. I suspect that it would take some time for the subject to train him/herself to sit or lay down in order to regain the ability to speak.

Addendum 12/23/2007:

Someone (Ritchie Annand) on the Expelled blog wrote that neurologists Marco Mumenthaler and Otto Appenzeller already falsified my hypothesis that the cerebellum does not generate speech. I disagree, of course. Here's the relevant excerpt from Neurologic Differential Diagnosis, section 2.11.3, Lesions of Basal Ganglia and Cerebellum:

With disorders of the cerebellum, speech is harmonically disturbed, irregular, loud and explosive. The speech disturbance in multiple sclerosis is due to foci in the cerebellum, and takes the form of staccato explosive speech with exaggerated pauses between parts of the sentences and words, as in scanning speech.

In my opinion, the observations of Mumenthaler et al lend credence to my claim. It makes sense that cerebellar damage should affect speech production as I pointed out above, but that is not evidence that the cerebellum generates speech. Since the motor cortex and Broca’s area normally rely on the cerebellum to attend to routine tasks (e.g., maintaining posture, walking, standing, etc…) when speaking, it is logical to expect that speech should be affected as a result of a cerebellar lesion. The motor cortex cannot multitask. Therefore, unless the cerebellum is helping, the motor cortex is forced to interrupt itself frequently to attend to important tasks. Hence the stacatto speech and exagerated pauses observed by Mumenthaler et al.

Since speech impairments are observed in patients with cerebellar damage, it is very easy to conclude that the cerebellum contributes to speech production. A cursory look at the neurological literature indicates that many have already reached this conclusion. I argue that this is not the case. Based on my research, I can confidently predict that the speech processing ability of subjects with cerebellar lesions should markedly improve when the subjects are lying down in a relaxed position. The reason is that there is no need for the brain to maintain posture (a normal cerebellar function) while the subject is in a relaxed position, in which case the motor cortex has more freedom to lend its undivided attention to speech production. It should be a fairly easy way to test this hypothesis.

If any of my readers know of someone with a speech impairment due to a cerebellar lesion, please ask him or her to lay down on a couch and relax. I predict that he/she will find it easier to speak as a result.

See also:

The next four posts in this series. Just click on Newer Post at the bottom of this page.

Tuesday, December 11, 2007

Christianity, Evolution and Falsifiability

Intelligent Design and the Demand for Falsifiable Predictions

One of the incessant demands from atheists and Darwinian evolutionists is that intelligent design proponents must provide falsifiable predictions in support of the ID hypothesis. This is a legitimate demand, in my opinion. Unless and until ID proponents come up with formal predictions that can be tested by other researchers, they do not have a leg to stand on.

My Take on the Design vs. Evolution Debate

I am a non-fundamentalist Christian evolutionist as opposed to a Darwinian evolutionist. In my opinion, it is not really evolution that is in dispute. There is no doubt that some form of evolution is happening now and has been happening for millions of years. What is in dispute is exactly how it happened. I disagree with the Darwinian stance regarding the origin of species. I believe that evolution was intelligently directed in the past through genetic engineering. I must add that I am not affiliated with the ID movement.

The way I understand it, most proponents of Darwinian evolution claim that the species originated as a result of random mutations and natural selection through sexual reproduction. They maintain that it happened naturally without intelligent intervention. Of course, as a Christian, I have to disagree with that stance, since it contradicts the Biblical teaching that the original species where created by God. The creation process obviously lasted millions of years (no, I don’t believe that God created the heavens and the earth in six twenty-four-hour days). Thus it is not surprising that the fossil record shows a progression in the sophistication of the species over time. Any creation process is necessarily an evolutionary process. The fact that biological research successfully relies on the evolutionary hypothesis is not surprising either but it is not evidence that evolution was not intelligently directed.

Falsifiability

I have no idea whether or not ID advocates have proposed any experimental test that could potentially falsify the design hypothesis and silence their critics. All I have is my own research based on Biblical metaphors. I take an indirect approach to ID falsifiability. I believe that the Bible contains amazing and revolutionary scientific information hidden in clever metaphors. I believe that the metaphors, once properly deciphered, can be used to make precise scientific predictions that can be tested in the laboratory. It follows that if any of these predictions can withstand falsification, they would lend credibility to Biblical claims regarding the origin of the species.

My critics can always argue that any interpretation of Biblical passages is highly suspect because the Bible can be interpreted to support any point of view and I agree. However, based on my research over the last twenty years, I feel sufficiently confident in my understanding of certain Biblical metaphors to make testable predictions about various characteristics of brain operation and organization. These are precise predictions about aspects of the brain (unknown to science) that I could not possibly have any knowledge of, since I am neither a neurobiologist nor do I have access to a neurobiological research lab. What follows is one such testable prediction about an aspect of the cerebellum that is currently unknown to neurobiologists and brain experts.

Falsifiable Biblical Prediction About the Cerebellum

According to my interpretation of the Biblical texts, the cerebellum is a supervised automaton. It is trained by the motor cortex to take over certain routine motor tasks whenever the basal ganglia and motor cortex are busy reasoning internally or engaging in some other motor activity. My understanding of the metaphorical messages to the church of Pergamum (Broca's area) and Laodicea (cerebellum) in the book of Revelation is that speech is always an attentional or volitional (as opposed to automatic) process that involves corrective feedback from the basal ganglia. The cerebellum is not directly involved in processing speech and language. The indication is that the cerebellum can have motor control over the entire body except the mouth, throat and tongue muscles. This means that activities like eating, chewing and swallowing are also excluded from cerebellar control.

How can this prediction be falsified? In my opinion, it suffices to examine the brain pathways that link the motor cortex with the cerebellum. The prediction is that there are no pathways between the cerebellum and any parts of the motor cortex that controls the mouth, speech, etc… Another way to falsify this prediction would be to use MRI images to observe cerebellar activities when a subject is speaking (in a relaxed position) and engaging in non-speech related activities. I predict that the data will support the claim that the cerebellum cannot produce speech.

Another interesting consequence to this prediction is that serious damage to the cerebellum should be accompanied by a loss of speech capability while the subject is engaged in other motor activities (e.g., walking). The reason is that the subject can no longer rely on the cerebellum for routine tasks (while speaking) and must consciously attend to them. We can only attend to one conscious task at a time. This is why the cerebellum is so important. I suspect that it would take some time for the subject to train him/herself to sit or lay down in order to regain the ability to speak.

More falsifiable predictions to come…