Temporal characteristics of the sensitivity-enhancing after-effects of fusimotor activity on spindle la afferents

The after-effects of fusimotor stimulation which enhance dynamic sensitivity of spindle Ia afferents have been further investigated. The response to small sinusoidal movements was increased during muscle lengthening, following stimulation of single static or dynamic γ-axons at resting length. This effect could be elicited by low rate stimulation during less than one second, and it persisted for up to two minutes. It might therefore be relevant for the control of spindle sensitivity during postural tasks.