Stimulus – response reflexes can respond to internal processes of the body and internal signals in the mind. And we are still trying to understand how these pathways work. I am especially interested in the way the brain organizes internal signals, especially the initiation of voluntary goal oriented movements and the connection between thoughts [thinking about moving] and outcome [actually moving].
The voluntary motor loop
Paul Johns BSc BM MSc FRCPath, in Clinical Neuroscience, 2014
Initiation of voluntary actions involves a basal ganglia loop that originates and terminates in the supplementary motor area (SMA) (Fig. 13.13; see also Ch. 3). Activity in the SMA and voluntary motor loop is facilitated by dopamine, which lowers the threshold for movement initiation. This helps to determine whether an intention to act is translated into an actual movement. Reduced activity in the SMA (due to striatal dopamine deficiency) is responsible for the akinesia (poverty of movement) in Parkinson’s disease.
The SMA is involved in self-initiated actions (e.g. throwing a ball, rising from a chair) rather than movements that occur in response to an external stimulus or trigger (e.g. catching a ball, stepping over a piece of chalk). This has been exploited with the creation of virtual reality glasses that provide artificial visual cues for parkinsonian patients (projections of horizontal lines to ‘step over’). This leads to improvement in gait initiation, stride length and pace, with fewer falls. In some cases, powerful emotions can overcome akinesia (Clinical Box 13.6).
▪Initiation of voluntary movement is associated with increased activity in the supplementary motor area (SMA) and voluntary motor loop, which is facilitated by dopamine.▪
The SMA is particularly involved in self-initiated (rather than externally triggered) actions and this type of movement is most affected in Parkinson’s disease.▪
In addition to the well-known (and best-understood) roles in motor control, the basal ganglia also contribute to numerous aspects of cognition, behaviour and mood.
It seems that that the Supplemental Motor Area is key to both the intention to act [thinking] and the ability to perform that self initiated action.
Paula does not suffer from Parkinson’s but she did have these Parkinson-ion features. When she was ill, Paula’s thoughts, her internal signals , containing her intention to speak or her intention to act , faded before she could put them into action. The signals were too weak to last long enough to create self initiated actions. She knew what she wanted to do…then the signal faded and she no longer remembered. . At first, she realized the signal faded and worried why…then the worry faded too. Till she thought of something else she wished to do. The FEAR that accompanied the weak signals were constant throughout, no matter what she was thinking and what she forgot. Paula remembers what is was like, it was completely freaky and very abnormal and so very unpleasant. And she could not explain because it made no sense anyway. Who suffers suddenly from weak thinking signals? Weak signals that inhibit or impair “self initiated actions”.
Like patients with Parkinson’s, Paula could respond to external stimuli; she could answer when spoken to or walk normally without bumping into things. She could also still use her accessory muscles to keep breathing .
The FEAR she felt could be due to external stimuli [being scared of being fired from her job] or her internal thoughts [why don’t I understand what I am reading?] or it could be due to shortness of breath that she was aware of only intermittently [then forgot] , a shortness of breath that was not visible to others because of her usual slow breathing rate. She could have felt fear because her minute ventilation [exchange of fresh air] was no longer sufficient due to a bunch of factors [she’d been sick with a variety of viruses and was continually exposed to higher levels of contaminants at work and was weakened by her loss of weight from a stomach bug. And she was going through normal hormonal changes of middle age [menopause].
One or all of these factors might have pushed her into a “mild” respiratory pump failure.
The experience of fear will result in the usual pattern of physical signs; faster heart rate, higher blood pressure, and faster breathing.
Paula did experience a faster heart rate, and a high blood pressure [had anyone bothered to check] but her breathing rate, already impossibly low, DID NOT RISE!
And this is the important clue that everyone, including Paula, missed.
Her breathing rate during sympathetic activation and extreme distress and fear remained depressed.
What she went through for a year was not psychological, it was a reaction to not being able to adjust her breathing rate to the increased respiratory load she was under.
And the way to discover the reason for the changes in her motor behaviour was to measure her respiratory rate and her other vital signs [HR, BP and Body Temperature].
And now you know.
Paula experienced a chronic delirium. There are three motor subtypes in delirium/ the hyperactive type of which, in our opinion, Mania is one example (pure agitation), the hypoactive type (pure lethargy), and the mixed (fluctuation between lethargy and agitation).
Paula’s agitation was internal, [it was unbearable, it was pure distress, pure fear] and externally she was awake but lethargic, she had no energy to stand or sit up straight, she had no energy to speak or move much- she stared into space a lot, the most she would do was pace as a result of her agitation.
This state looks externally like depression.
Internally it feels like fear and mental confusion.
The physical exam with careful measurement of the vital signs [especially respiratory rate] will tell you the diagnosis.
When doctors say, listen to your patient, he/she will tell you the diagnosis; they are talking the language of medicine not psychology. The mean listen as in measure the vital signs and look at the body condition and circulation of the patient and possible reasons for the external lethargy and internal agitation.
Let us look at the Updated Motor Signs of Delirium……