Biomedical subjects

R A Sieb

Publications and source records attributed to R A Sieb.

4 recordsLinked to original sources

PubMed1990

A brain mechanism for attention.

Attention is directed or focussed consciousness. Consciousness is a subjective sensation produced by the simultaneous activation of discrete neurophysiological systems. These are the alerting, awareness, affect, arousal, and attention systems. The process begins with the subcortical scanning of sensory stimuli for affect and significance via pleasure, pain and tension systems. The perceptions then pass to the Thalamus for further scanning and concentration into one sensory modality by Thalamic-Prefrontal-Thalamic reflex inhibition. The unimodal, significant perceptions then activate engrams in the Posterior Inferior Temporal Cortex, the Posterior Inferior Parietal Cortex, and the Posterior and Anterior Association Cortex. These areas project to the Prefrontal Association Cortex (PAC). The PAC inactivates sensory scanning systems causing fixation. The PAC also sends signals to the Hippocampus, which are gated by Septal and Hippocampal generated theta activity in the Hippocampus. This transiently interrupts the blanket inhibition of orientation, alertness, awareness, and arousal produced by the theta activity via the Hypothalamus. As a result of the above mechanisms, only one sensory stimulus activates the orientation, alerting, awareness, arousal, and cognitive systems and hence focussed attention occurs. Focussed attention can also be used to explain the initiation of voluntary movements.

Arousal↗

PubMed1989

Proposed mechanisms for cerebellar coordination, stabilization and monitoring of movements and posture.

In this paper cerebellar mechanisms have been proposed for the coordination of all movements, for the learning effect of training on movements, for the effect of mental set on posture and voluntary movements, for the detection of velocity and acceleration, and for the stabilization of movements and posture. Coordination of agonist, antagonist, fixation and synergistic muscles during a movement could occur via a cerebellar matrix which connects agonist efferent feedback from the Motor Cortex to the appropriate antagonist motor cortical neurons. Improved efficiency through repetition (learning) occurs through suggested changes at the molecular and synaptic levels. The Inferior O-live-Climbing Fibre System is seen as a dynamic oscillator; indicating when a movement begins, its velocity and acceleration, and its stability. According to this view, the cerebellum stabilizes movements, and adds the effect of mental set on posture and voluntary movements, by inducing changes in the gain of stretch reflexes. Inhibitory interneurons add versatility to movements, while excitatory collaterals from cerebellar afferents directly to cerebellar deep nuclei improve sensitivity of the system. These mechanisms work for all movements whether active, passive, or reflexive.

Action Potentials↗

PubMed1987

A proposed mechanism for the production of skeletalmotor positioning movements by the basal ganglia.

A programming function for the Basal Ganglia is suggested by implicating them in the production of positioning movements during directed skeletalmotor movements. The Association Cortex (especially the Prefrontal) sends a signal which is an internal representation of the desired end position of a movement to the Caudate. The Sensorimotor Cortex sends feedback from the commands for the primary movement to the Putamen, this representing the end position to be attained by the primary movement. These two signals are integrated in the Lateral Pallidal Segment producing a signal coding the magnitude and possibly the timing of positioning movements. This signal is sent to the Subthalamic Nucleus, which distributes it to the two main output areas of the Basal Ganglia and hence to affect motor and postural pathways.

Animals↗

PubMed1987

Skeletomotor subsystems.

Skeletomotor movements can be divided into five subsystems, each having its own independent mechanism and purpose. The subsystems are: 1. Reflex 2. Position 3. Velocity 4. Pursuit 5. Simultaneous. Reflex movements are rapid, stereotyped, inflexible and specific in terms of stimulus and response. Position movements are made to a target or certain position, with or without a load. A mechanism is proposed by which the Basal Ganglia program positioning movements into the primary movement and any load is compensated for by the stretch reflexes. Velocity movements are throwing movements and a mechanism is proposed by which the Cerebellum programs velocity into the basic, primary movement. A mechanism for Pursuit movements is proposed by which sensory and pursuit neurons activate velocity neurons whose activity drives the motor pathways to make pursuit movements. Simultaneous movements could be under the direction of the Prefrontal Cortex utilizing sensory feedback and interhemispheric transfer of information. A subcortical or cerebellar pattern generator could be set up for movements such as walking and running. The purpose of this division is to provide a guide for research and to aid in the understanding and treatment of diseases and injuries that affect the motor system.

Animals↗