13:00: Opening by the Moderator Ole Kæseler Andersen
13:05: PhD lecture by Mauricio Henrich
14:00: Questions and comments from the Committee
15:30: Questions and comments from the audience at the Moderator’s discretion
16:00 Conclusion of the session by the Moderator
The Faculty Council has appointed the following adjudication committee to evaluate the thesis and the associated lecture:
Mariano Serrao, Department Medico-Surgical Sciences and Biotechnologies, Sapienza University of Rome.
Ruth Defrin, Department Physical Therapy, Tel-Aviv University, Tel-Aviv, Israel.
Associate Professor Andrew James Thomas Stevenson, Department of Health Science and Technology, Aalborg University
Professor Ole Kæseler Andersen, Department of Health Science and Technology, Aalborg University
HOW TO PARTICIPATE
The Ph.D. Defense is organized as a hybrid event you can participate digitally via Zoom or physical presence.
Location: Aalborg University – Room 4-111, Niels Jernes Vej 14, Aalborg East
Please click here to participate via Zoom.
Meeting ID: 648 8904 1017
The somatosensory system plays a predominant role in building an internal representation of the outer world and the current state of the body. To this purpose, sensing organs continuosly translate physical properties of the environement into electrical signals that are conveyed to the brain to produce a cognitive perception of the surroundings. In addition to the cognitive response, humans have defensive mechanisms implemented within the CNS. These mechanisms allow rapid defense from potentially harmful stimuli to preserve homeostasis and avoid tissue damage. One example of such defensive mechanism is the Nociceptive Withdrawal Reflex (NWR). The NWR is a polysynaptic spinal reflex that integrates information from sensory afferent fibers, proprioceptive fibers, together with descending modulatory activity, into an efficient withdrawal response of the exposed tissue. The optimal withdrawal response coordinates both lower limbs, the trunk, and potentially the entire body, to defend the exposed tissue while preserving balance, according to the current motor needs. In order to do this, temporal and spatial information from the external stimuli needs to be integrated, encoded, and interpreted. Observations of spatial and temporal integration of nociception has been reported in the literature based on pain intensity ratings and other psychometrical variables (i.e.: location, radiation, quality). Whether and how the NWR pathway exploit tempo spatial information of the stimulus, and how that information become available to cognitive processes, remains to be clarified.
This thesis synthesizes the results of a PhD project that aimed at studying spinal spatial and temporal integration of nociception. The project was motivated by recent evidence suggesting that lateral inhibitory mechanisms play a significant role in the spatial integration of multiple nociceptive stimuli applied in a small area of skin of healthy subjects. As early animal studies have shown spinal neurons encoding spatial characteristics of the stimulus, a spinal-specific approach was expected to provide relevant and novel evidence about the involved integrative mechanisms in humans. The primary outcome of all studies congregated in this thesis was the magnitude of the NWR, which was complemented by other psychophysical outcomes. Additionally, the modulation of this spinal integration through descending control initiated by cognitive activity was investigated.
In particular, the first study on which this thesis is based was designed as a descriptive study that aimed at investigating spatial aspects of the integration of simultaneous nociceptive stimuli. Simultaneous stimulation included stimuli with varying inter electrode distances (IEDs) applied to five electrodes on the sole of the foot. This study showed evidence of how spatial information of the stimuli is integrated in the NWR pathway. This integration seemed to have a functional, behavioral role according to the modular organization of the NWR. Evidence of spatial summation on both: perceived intensity and NWR outcomes, was presented and discussed. The second study focused on how temporal information is integrated into an efficient withdrawal response. In this study, a temporal delay of different durations was used, together with single and simultaneous stimuli. The results provided evidence on how temporal and spatial aspects of the stimulus are integrated to produce a reflex and a perceptual response that is functional to the defensive role of the NWR. Differences between muscles involved in the NWR were studied and discussed. Lastly, the third study assessed whether a purely cognitive task modulates integration of simultaneous stimulation at spinal level. Two cognitive manipulations were used, aiming at shifting the attention of the subject away or into the stimulated site. Results showed that the NWR is significantly facilitated when subject are distracted from the stimulated site. The integration of simultaneous stimulation, however, seem not to be affected significantly.
In conclusion, the assessment of the NWR and its modulation by cognitive tasks provided novel evidence on the spatial and temporal integration of nociception at the spinal level. The NWR pathway simultaneously integrates temporal and spatial information of the aversive stimuli, to elaborate an optimal defensive response. This net reflex response can be explained by a modular organization of the NWR with a functional role that likely involve the coordination of several muscles, according to the defensive needs. Results of the perceptual response (pain intensity) and the behavioral response (NWR) showed differential processing of information between the pain and the NWR pathways. This suggest that the NWR magnitude cannot be directly used as a proxy of pain intensity (particularly with complex stimuli) or spinal nociception.
Three studies and four conference abstracts disseminate the experimental work that was carried out during this project. All the experiments were conducted at the Center of Neuroplasticity and Pain, Aalborg University, Denmark. The work was supported by the Danish National Research Foundation (DNRF121), and by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 754465