Conscious, Unconscious & Involuntary Control of Locomotion & Comparable Stereotyped Motor Behaviors

Abstract

It is generally believed that voluntary movements are controlled by brain structures. Signals from cortical areas (e.g., primary motor cortex) are specifically considered to underlie the expression of volitional motor behaviors such as pointing finger or hand reaching for a bottle. However, there are also compelling evidence and breakthrough findings demonstrating that some motor behaviors, especially rhythmic and/or stereotyped, can also be unconsciously and/or involuntary controlled for the most part. For instance, the classical Ia reflex, a simple stereotyped, monosynaptic, and involuntary mediated motor response can be consciously felt in some circumstances whereas the Ib disynaptic reflex is always completely involuntary and unconscious. The pioneering work of Graham Brown in the early 1900s provided evidence of involuntary control mechanisms even for more complex stereotyped behaviors such as basic walking or running that can be mediated in complete absence of supraspinal inputs. In the 70s, Grillner and Zangger clearly showed that basic locomotor activities can indeed be induced without brain structures and sensory inputs in completely decerebrate and rhizotomized animals. Other findings showed subsequently comparable brainstem and/or spinal control mechanisms for many other complex rhythmic stereotyped motor behaviors such as mastication, deglutition, respiration, micturition, defecation, and ejaculation. The relevance of such findings for research on the neural control of movements as well as on the role of neural correlates of mindful (e.g., DMN, DAN, etc.) movements is discussed.