“To move things is all that mankind can do, and for this the sole executant is a muscle, whether it be whispering a syllable or felling a forest.” This quote from Charles S. Sherrington couches the fact that most of the processing in the nervous system is dedicated to producing movement. The final expression of most cognitive and emotional processes includes motor actions.” Physiological Review : Current Principles of Motor Control, with Special Reference to Vertebrate Locomotion Sten Grillner and Abdeljabbar El Manira 18 NOV 2019
The vertebrate control of locomotion involves all levels of the nervous system from cortex to the spinal cord. Here, we aim to cover all main aspects of this complex behavior, from the operation of the microcircuits in the spinal cord to the systems and behavioral levels and extend from mammalian locomotion to the basic undulatory movements of lamprey and fish. The cellular basis of propulsion represents the core of the control system, and it involves the spinal central pattern generator networks (CPGs) controlling the timing of different muscles, the sensory compensation for perturbations, and the brain stem command systems controlling the level of activity of the CPGs and the speed of locomotion. The forebrain and in particular the basal ganglia are involved in determining which motor programs should be recruited at a given point of time and can both initiate and stop locomotor activity. The propulsive control system needs to be integrated with the postural control system to maintain body orientation. Moreover, the locomotor movements need to be steered so that the subject approaches the goal of the locomotor episode, or avoids colliding with elements in the environment or simply escapes at high speed. These different aspects will all be covered in the review.
“ To initiate a movement in a behavioral context, the brain needs to determine the overall goal of the movement, then select which circuits to activate, and finally execute the movements with precise timing, speed, and coordination.” Physiological Review : Current Principles of Motor Control, with Special Reference to Vertebrate Locomotion Sten Grillner and Abdeljabbar El Manira 18 NOV 2019
In the case of Paula, during her attack of psychomotor retardation [ a sign of major depression, bipolar depression, or hypoactive delirium ], she remembers that she could not think her thought… [eg. “I really need to call a doctor”] ….long enough in order to initiate her movement in a behavioral context. She could not “ determine the overall goal of the movement, then select which circuits to activate, and finally execute the movements at all .” Instead she just stood there perplexed. It was a very strange experience and it occurred all day whenever she tried to enact her thought which vanished into thin air, before she could do anything or say anything. This was very disabling, indeed. It was also very private, since no one could see her thought vanish into thin air. It was really horrible. [until she forgot that it occurred because that thought also vanished]. The result? She stood around a lot or sat around a lot vacuously.
Definition : vac·u·ous
1.a. Lacking intelligence; stupid or empty-headed. b. Devoid of substance or meaning; vapid or inane: a vacuous comment c. Devoid of expression; vacant: a vacuous stare.
.2. Lacking serious purpose or occupation; idle:
No one could tell that this “idleness” empty headedness and “lack of facial expression” was involuntary.
It was and is anyone’s worse nightmare!
She simply woke up this way and stayed this way for over a year.
“The main structures of importance for the control of goal-oriented movements in the forebrain are the cortex, basal ganglia, including the dopamine system, and thalamus.” Physiological Review : Current Principles of Motor Control, with Special Reference to Vertebrate Locomotion Sten Grillner and Abdeljabbar El Manira 18 NOV 2019
The basal ganglia are situated at the base of the forebrain and top of the midbrain. Basal ganglia are strongly interconnected with the cerebral cortex, thalamus, and brainstem, as well as several other brain areas.
Paula could still respond to external commands and stimuli [albeit in a rather concrete manner – more like a 10 year old]. Indeed, responding to command or idly walking around takes very little thought…
For many aspects ” of locomotion, motor cortex is not needed.
Actually, in mammals including cats and rodents, the motor cortex can be removed (see Ref. 284) without significant effects. Even the entire cortex can be removed without any visible effects on most aspects of basic motor behavior (49, 406, 468). Without all parts of cortex, a cat can still walk around, explore the environment, search for food, and survive for years in a laboratory environment. Under these conditions, the basal ganglia remain intact and can apparently still handle the selection of behavior, that is, to initiate movements appropriate to the external or internal demands of the animal.” Current Principles of Motor Control, with Special Reference to Vertebrate Locomotion Sten Grillner and Abdeljabbar El Manira 18 NOV 2019
The explanation above tells us why it is so hard to detect what is wrong with any animal; Imagine being able to do most things without a frontal cortex! That explains a lot, but still, Paula was not able to initiate any goal oriented movement, because of memory issues……maybe her basal ganglia was not intact? The basal ganglia communicates to the Supplemental Motor area, an area of the brain we discussed in a recent past blogpost, the SMA is also responsible for voluntary movement.
The supplemental motor area is also important to the proper function of working memory. Front. Psychol., 23 May 2018 https://doi.org/10.3389/fpsyg.2018.00765 Working Memory Deficits After Lesions Involving the Supplementary Motor Area Alba Cañas1, Montserrat Juncadella1, Ruth Lau2, Andreu Gabarrós2,3 and Mireia Hernández3,4,5*
Paula’s working memory was impaired. . This is why when asked, Paula could not remember her address during her illness. What is more, Paula did not know that she would not be able to remember her address, whenever you asked. Pretty freaky no? Downright scary! Maybe her Supplemental Motor Area was affected And the sign that she was recovering [after more than a year] was the return of her ability to remember her address and her ability to know that she knew her address. Only then was she able to return to work and function normally.
This is truly a complex problem, especially when the only person that knows there is a physical problem involving mind, working memory and goal oriented behavior is unable to tell anyone..
The SMA [supplemental motor area is at the tippy top of the brain. It i possible that increased inter-cranial pressure [from hypercapnia-see past blogs] would cause squishing from the inside of the top of skull, enough to reversibly [once the pressure eased up] mess up working memory and result in motor slowing. Who knows?
No one thought to test her muscle function, although if one thinks about it, it makes perfect sense. Psychomotor retardation could also come from muscle weakness. Perhaps affecting the respiratory muscles and breathing.
She had been sick with various viruses before the attack, she had lost weight, she looked poorly, [sickly], she was very pale, her voice was weaker, she suddenly used only 2-3 word sentences, …in retrospect, it is possible that she was experiencing skeletal and cardiac [myopathy] muscle changes impairing her ability to speak, move and perhaps even breathe. [breathing requires work of the skeletal muscles].
This may explain why reduced grip strength [of the hand] and reduced walking distance are linked to cognitive impairment; not because thinking involves muscle, but because all vital functions [moving, swallowing, coughing, breathing [the ventilatory pump moving air in and out of the lungs], all depend on the health of the skeletal muscles.
BMC Geriatr . 2019 Jul 5;19(1):186. doi: 10.1186/s12877-019-1199-7. Role of gait speed and grip strength in predicting 10-year cognitive decline among community-dwelling older people Ming-Yueh Chou 1 2 3 4 5, Yukiko Nishita 6, Takeshi Nakagawa 7 8, Chikako Tange 7, Makiko Tomida 7, Hiroshi Shimokata 7 9, Rei Otsuka 10, Liang-Kung Chen 2 3 11, Hidenori Arai 4 PMID: 31277579 PMCID: PMC6612180 DOI: 10.1186/s12877-019-1199-7
Although most of the studies regarding cognitive decline and gait speed and grip strength have been done on the elderly, the same may be true if a young adult becomes weakened by illness or injury.
And doctors do not check for impairment of muscle function.
This is something that nurses and rehabilitation specialists look at, especially during rehabilitation after any illness or accident.
So psychomotor retardation of major depression, hypoactive delirium or reversible [possibly] dementia might all be related to muscle strength and muscle strength is important for the respiratory pump to work at capacity in order to avoid hypercapnia which is one of the [unlooked for] causes of mental confusion. Published: 22 December 2014 Prognostic value of physical function tests: hand grip strength and six-minute walking test in elderly hospitalized patients Esther Martín-Ponce, Iván Hernández-Betancor, Emilio González-Reimers, Rubén Hernández-Luis, Antonio Martínez-Riera & Francisco Santolaria
And, if you read about Paula and her respiratory defect and her good enough minute ventilation in health , then ask yourself what will happen if she becomes ill, undernourished and weaker? Do you think that her minute ventilation will remain sufficient for proper elimination of CO2 in the blood? Do you think that this might explain the change to her voice [speaking requires normal function of the muscles], her mask like face [related to weakened facial muscles?] and her inability to speak more than 2-3 words and her extra effort it took her to move her mouth properly to say those few words?
How do you think she might have done on gait speed or grip strength?
Think about that! These tests are easy to do. So is counting respiratory rate at rest. In young people and the elderly. Muscle weakness [temporary or chronic] can happen anytime after an injury or surgery or blood loss or iron deficiency or thiamine deficiency or inflammatory illness or infection or period of malnutrition.