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