رابطه بین تفاوت های جانبی در دمای پرده صماخ و تکانشگری رفتاری

In this study lateral differences in tympanic membrane temperature (TTy) were explored as a correlate of either impulsive or cautious responding in Go–No-Go tasks. Thirty-two women and men performed two sustained attention to response tasks (Go–No-Go tasks). Those with warmer right in comparison to left tympanic membranes were more cautious, and those with warmer left in comparison to right tympanic membranes were more impulsive. This finding is in line with previous research and theory indicating a hemispheric bias for active and passive behavior. TTy may be a useful addition to the techniques employed by neuropsychologists.

TTy) may be a useful physiological metric for scientists and clinicians interested in the relationships between brain laterality and behavior. TTy has been used recently as a non-invasive and inexpensive indicator of lateralized changes in cerebral blood flow during cognitive tasks ( Cherbuin and Brinkman, 2004, Cherbuin and Brinkman, 2007, Helton et al., 2009, Helton et al., 2009 and Hopkins and Fowler, 1998). Changes in cerebral blood flow influence tympanic membrane blood perfusion and temperature ( Sukstanskii & Yablonskiy, 2006). A source of confusion in the literature, however, regarding tympanic temperature is the distinction between differences in TTybetween-subjects and difference in TTywithin-subjects. As discussed by Zelenski and Larsen (2000), relationships can be within-subjects or between-subjects and these represent state or trait relationships respectively. Within-subject relationships are accounted by differences between states over time or over measurement occasions. These relationships essentially remove between-subjects variance by estimating change within-subjects, for example, from a control or resting baseline. The state information is hopefully not confounded by individual differences, as the initial individual differences between-subjects are held constant. The person essentially serves as their own control. Under normo-thermic circumstances the brain is warmer than the incoming blood as the brain is both metabolically active and well insulated from the environment inside the enclosed skull. An increase of blood flow from the relatively cooler body reduces TTy relative to a baseline measure, whereas a decrease in blood flow from the body elevates TTy relative to a baseline measure. In studies focusing on within-subjects changes (for example Cherbuin and Brinkman, 2004, Cherbuin and Brinkman, 2007, Helton et al., 2009, Helton et al., 2009 and Hopkins and Fowler, 1998), therefore increased TTy relative to a resting baseline measure is a marker of reduced cerebral blood flow and decreased TTy is a marker of increased cerebral blood flow. Between-subjects relationships, however, represent differences between individuals’ average levels on the measure, or trait differences. These relationships are calculated by collapsing the individuals’ data over time (e.g. averaging within-subjects), thus eliminating variance due to states (or within-subjects differences). While changes in TTy from baseline recordings, within-subjects differences, may reflect changes in cortical activation during tasks, consistent between—subjects differences of right and left TTy may reflect underlying differences in cerebral lateralization amongst individuals due to trait differences ( Boyce et al., 2002). Since the brain is well insulated from the environment, a relative difference in residual heat buildup would occur if there is a consistent difference in lateral metabolic cerebral activity. In between-subjects studies a consistent lateralized heat buildup should be reflected in average ipsilateral TTy. A consistent elevated temperature in one tympanum or the other may, therefore, reflect overall greater resting or residual activation in the ipsilateral hemisphere; cortical temperature is highly correlated with TTy in the ipsilateral ear ( Mariak et al., 2003 and Schuman et al., 1999). Indeed Boyce et al. (2002) demonstrated that warmer left TTy was associated with approach behavior, whereas warmer right TTy was associated with passive behavior in children. In general, active states lead to greater left hemisphere activation and passive states lead to greater right hemisphere activation ( Davidson, 2000, Gray, 2001, Harmon-Jones and Allen, 1998 and Sutton and Davidson, 1997). Originally this lateral asymmetry was framed as reflecting a difference in motivational direction between the hemispheres: approach versus withdrawal. More recent work has instead framed this distinction not in terms of motivation direction, but in terms of activation–inhibition, with left hemisphere activation reflecting active, impulsive or risk-taking behavior and right hemisphere activation reflecting passive, cautious or inhibitory behavior ( Clark et al., 2003, Drake and Myers, 2006, Fecteau et al., 2007, Gianotti et al., 2009, Knoch et al., 2006, Miller and Milner, 1985, Wacker et al., 2008 and Xue et al., 2008). Depressed mothers and their offspring, for example, have greater right hemisphere EEG activity than non-depressed controls ( Diego, Jones, & Field, 2010) and patients with right hemisphere lesions prefer risky decisions ( Clark et al., 2003). Given the lateralization of active–impulsive and passive-cautious states, adults with relatively greater left hemisphere activation and thus relatively elevated left TTy should be more impulsive (active). This should be the case when examined with averaged TTy as this measure should reflect consistent between-subjects differences in left lateral activation. If a person has a consistent left hemisphere activation bias there should be an increased heat buildup reflected in the person’s left TTy. Individuals with relatively greater right hemisphere activation and thus elevated right TTy should instead be more cautious. If a person has a consistent right hemisphere activation bias there should be an increased heat buildup reflected in the person’s right TTy. In the present study, this was investigated by examining the association between lateral differences in TTy and performance on the sustained attention to response task (SART; Robertson, Manly, Andrade, Baddeley, & Yiend, 1997). SARTs require participants to trade-off the speed of a Go response with accuracy in withholding to No-Go stimuli. The faster one responds to the Go stimuli, the more likely one is to press inappropriately to the No-Go stimuli ( Helton, 2009). The SART, therefore, provides an excellent means to test the association between lateral differences in TTy and the behavioral continuum between impulsive and cautious. People with relatively elevated left TTy should make faster responses to the Go stimuli but also make more errors of commission than people with relatively elevated right TTy.