Interhemispheric balance sets nostril differences in color-induced nasal thermal judgments.

Sniffing out of sight always the same colorless and odorless solution containing no thermal agents while viewing a bottle with colored water increases sensitivity of the left nostril/right hemisphere (RH) for warming sensations and sensitivity of the right nostril/left hemisphere (LH) for cooling sensations. It is likely that engagement in a temperature judgment task and the development of specific expectancies due to the presence of color cues alter and enhance processing in brain areas involved in thermosensory processing. The lateralized patterns thus intimate hemispheric specialization for thermosensory processing probably originating in reciprocal inhibition that confers balance between the hemispheres. If the inhibition-balance hypothesis were correct then the more the left nostril proves sensitive to warming the more the right nostril would prove sensitive to cooling. One hundred and ninety one healthy volunteers were tested here. The left nostril dominance for warming and the right dominance for cooling were replicated once more. The dominance of the left nostril for warming (left minus right nostril) correlated highly with the dominance of the left nostril to cooling (right minus left nostril) and the individual patterns of results were distributed along an axis starting from the expected left nostril/warming - right nostril/cooling pattern and ending at the opposite left nostril/cooling - right nostril/warming pattern. Furthermore, the point where the left nostril dominance for warming responses dropped and inverted perfectly coincided with the point where the right nostril dominance for cooling responses inverted too. Such a good continuum between the expected and the opposite patterns supports the inhibition-balance hypothesis. Finally, 66% of subjects exhibited the expected left-warming/right-cooling pattern suggesting, therefore, that, despite this continuum, there is a dominant lateral specialization for temperature processing.

Hot colors: the nature and specificity of color-induced nasal thermal sensations.

The nature of the recently discovered color-induced nasal thermal sensations was investigated in four Experiments. Subjects were required to fixate a bottle containing a red or green solution presented centrally (Exp1 and Exp4) or laterally (Exp2) and to sniff another bottle, always the same one, but which they were not allowed to see, containing 10 ml of a colorless, odorless and trigeminal-free solution. Each nostril was tested separately, and subjects were asked whether the sniffed solution induced warming or cooling sensations (plus an ambient sensation in Exp4) in the nasal cavity. The results of Experiments 1 and 2 confirmed the warming/left nostril-cooling/right nostril dissociation, suggesting the existence of different lateralized processes for thermal processing. However, Experiment 2 failed to demonstrate dominance of warming responses when subjects' eyes were directed to the left or cooling responses when they were directed to the right. Nor did gaze direction interact with the tested nostril. This suggests that the color-induced thermal sensations are specifically related to the nasal trigeminal system, rather than a general process related to general hemispheric activity. When the exposed bottles were colorless (Exp3), no lateralized patterns were observed, suggesting, in combination with the results of Experiments 1 and 2, that both color cues and nasal stimulations are necessary for lateralized patterns to arise. Rendering the temperature judgment even more difficult (Exp4), made the lateralized patterns shift towards the associated (i.e., ambient) responses. The results are discussed in a general framework which considers that, even in the absence of real thermal stimulus, preparing to process thermal stimuli in the nasal cavity may activate the underlying lateralized neural mechanisms, and that those mechanisms are reflected in the responses.