Postural responses explored through classical conditioning

• Published in: Neuroscience Vol. 164; no. 3; pp. 986 - 997
• Main Authors: Campbell, A.D, Dakin, C.J, Carpenter, M.G
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 15.12.2009; Elsevier
• Subjects: Acoustic Stimulation; Adult; balance; Biological and medical sciences; Conditioning (Psychology) - physiology; Cues; Electromyography; Extinction, Psychological - physiology; Feedback, Sensory - physiology; Female; Fundamental and applied biological sciences. Psychology; Humans; kinematics; Male; Muscle Contraction - physiology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; Neurology; Neuropsychological Tests; Postural Balance - physiology; Posture - physiology; posturography; Reflex - physiology; Reflex, Startle - physiology; Vertebrates: nervous system and sense organs; Young Adult; PR; posturography; CNS; stimulus onset asynchrony; tibialis anterior; SD; conditioned stimulus; balance; UR; EMG; US; SOA; unconditioned response; kinematics; LMN; TA; central nervous system; CS; SOL; unconditioned stimulus; RF; electromyography; A/D; rectus femoris; lower motoneuron; analog-to-digital; postural response; standard deviation; soleus; Electrophysiology; Electromyography; Classical conditioning
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/j.neuroscience.2009.07.042

Abstract The purpose of the study was to determine whether the central nervous system (CNS) requires the sensory feedback generated by balance perturbations in order to trigger postural responses (PRs). In Experiment 1, twenty-one participants experienced toes-up support-surface tilts in two blocks. Control blocks involved unexpected balance perturbations whereas an auditory tone cued the onset of balance perturbations in Conditioning blocks. A single Cue-Only trial followed each block (Cue-OnlyControl and Cue-OnlyConditioning trials) in the absence of balance perturbations. Cue-OnlyConditioning trials were used to determine whether postural perturbations were required in order to trigger PRs. Counter-balancing the order of Control and Conditioning blocks allowed Cue-OnlyControl trials to examine both the audio–spinal/acoustic startle effects of the auditory cue and the carryover effects of the initial conditioning procedure. In Experiment 2, six participants first experienced five consecutive Tone-Only trials that were followed by twenty-five conditioning trials. After conditioning, five Tone-Only trials were again presented consecutively to first elicit and then extinguish the conditioned PRs. Surface electromyography (EMG) recorded muscle activity in soleus (SOL), tibialis anterior (TA) and rectus femoris (RF). EMG onset latencies and amplitudes were calculated together with the onset latency, peak and time-to-peak of shank angular accelerations. Results indicated that an auditory cue could be conditioned to initiate PRs in multiple muscles without balance-relevant sensory triggers generated by balance perturbations. Postural synergies involving excitation of TA and RF and inhibition of SOL were observed following the Cue-OnlyConditioning trials that resulted in shank angular accelerations in the direction required to counter the expected toes-up tilt. Postural synergies were triggered in response to the auditory cue even 15 min post-conditioning. Furthermore, conditioned PRs were quickly extinguished as participants became unresponsive by the third trial in extinction. In conclusion, our results reveal that the CNS does not require sensory feedback from postural perturbations in order to trigger PRs.