Evaluation of inhibitory spinal pathways in introverts and extroverts

• Grant number: 13/16276-5
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2014
• End date: November 03, 2015
• Field of knowledge: Engineering - Biomedical Engineering - Bioengineering
• Principal Investigator: Fernando Henrique Magalhães
• Grantee: Jéssica Rodriguez Lara
• Host Institution: Escola de Artes, Ciências e Humanidades (EACH). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated scholarship(s): 15/00367-7 - Assessing neuromuscular plasticity associated with rhythmic arm and leg cycling by means of spinal reflex pathways evaluation in chronic stroke, BE.EP.IC

Abstract

The personality trait of extraversion (a personality dimension associated with sociability) has been identified as an important feature of individual differences. For example, differences between introverts and extroverts were reported in the field of motor behavior, based on the analysis of the performance of these individuals in a wide variety of experimental paradigms involving motor tasks. However, few studies have been conducted to investigate the possible neurophysiological mechanisms associated with such differences in motor behavior. Among them, two interesting studies have shown lower levels of motoneuron excitability in extroverts as compared to introverts. Besides putative differences associated with supraspinal (e.g. cortical) motor commands, a variety of spinal mechanisms may be associated, jointly or separately, with the different levels of motoneuronal excitability in introverts and extraverts, for instance, the ongoing state of presynaptic inhibition, homosynaptic depression or reciprocal inhibition. In this vein, thanks to advances in the knowledge about these spinal circuits and to the development of electrophysiological techniques such as the assessment of H-reflex through a paired-pulse stimulation paradigm (also known as conditioning-test pulse paradigm), it is possible to employ non-invasive protocols to selectively explore the transmission within a variety of human spinal cord pathways so as to investigate the possible role of specific spinal mechanisms on the individual differences associated with motoneuronal excitability in introverts and extraverts. Therefore, the aim of this project is to evaluate, through the H-reflex of the soleus muscle conditioned by stimuli applied to the common peroneal nerve (i.e. the nerve associated with the antagonist muscle, tibialis anterior), the levels of excitability of spinal inhibitory pathways (specifically the levels of reciprocal inhibition, presynaptic inhibition and homosynaptic depression) in introverts and extroverts subjects. Besides allowing a better understanding on the neurophysiology of neuromuscular control in introverts and extraverts, the results may indicate differential physical training strategies and therapeutic interventions based on the individual personality trait.