The pyramidal syndrome

The hallmark of lesions of the motor cortex or its descending fibres in the human is the pyramidal syndrome. It is characterized by deficient force generation and impairment of selective control of the fingers. Recovery is better in proximal than in distal muscles, which almost regain their former capacity, even in cases with complete pyramidal tract (PT) transection. Within the remaining range, force control is good as is sensory guidance. There is no disturbance of movement initiation, preparation or of specifications such as movement direction, and there are no apractic phenomena.

It is an old controversy whether the increase in tone and reflexes, which is often regarded as part of the pyramidal syndrome, is due to the damage of motor cortex and its descending fibres or whether it indicates the impairment of more rostral areas. Ablation studies in monkeys and apes showed that excisions restricted to area 4 led to an initially flaccid paresis, later resolving into a state of approximately normal tonus. Hines (1929) found spasticity only after excisions involving the anterior part of area 4 and called this ‘suppressor strip’ or area 4s. Electrical stimulation of this strip yielded muscle relaxation. For the mediation of this inhibitory action McCulloch, Graf & Magoun (1946) described a separate non-pyramidal cortico-reticular pathway projecting from area 4s to the brainstem. Although such an inhibitory zone has not been confirmed by subsequent studies, other authors have associated spasticity with more anterior lesions centring on the superior precentral sulcus in the premotor area of the macaque cortex (Fulton & Kennard, 1934; Denny-Brown & Botterell, 1948; Woolsey et al., 1952).