Speed-cohesion trade-offs in collective decision making in ants and the concept of precision in animal behaviour

In decision making, speed-accuracy trade-offs are well known and often inevitable because accuracy depends on being well informed and gathering information takes time. However, trade-offs between speed and cohesion, that is the degree to which a group remains together as a single entity, as a result of their decision making, have been comparatively neglected. We combine theory and experimentation to show that in decision-making systems, speed-cohesion trade-offs are a natural complement to speed-accuracy trade-offs and are therefore of general importance. We then analyse the decision performance of 32 rock ant, Temnothorax albipennis, colonies in experiments in which accuracy of collective decision making was held constant, but time urgency varied. These experiments reveal for the first time an adaptive speed-cohesion trade-off in collective decision making and how this is achieved. In accord with different time constraints, colonies can decide quickly, at the cost of social unity, or they can decide slowly with much greater cohesion. We discuss the similarity between cohesion and the term precision as used in statistics and engineering. This emphasizes the generality of speed versus cohesion/precision trade-offs in decision making and decision implementation in other fields within animal behaviour such as sexually selected motor displays and even certain aspects of birdsong. We also suggest that speed versus precision trade-offs may occur when individuals within a group need to synchronize their activity, and in collective navigation, cooperative hunting and in certain escape behaviours.

Biomechanical concept and clinical outcome of dual mobility cups

La luxation d'une prothèse totale de la hanche est une complication majeure en termes de morbidité pour le patient et des coûts pour le système de santé. Cette complication est retrouvée entre 2 à 3% selon les séries (1-3) pour des prothèses primaires, et beaucoup plus élevée suite à des révisions. Pour remédier à ce problème, des systèmes de prothèses contraintes sont une option, cependant associés à des descellements fréquents entre 10 à 26 % selon les séries (4-6). Ces échecs étant en partie expliqués par une usure rapide des surfaces de frottements due aux fortes contraintes, mais également par les contraintes cupule-os occasionnant des descellements mécaniques (7). Par conséquent, pour augmenter la stabilité, tout en évitant les contraintes sur le couple de frottement, Bousquet développe, en 1976, une prothèse totale de hanche « à double mobilité ». Ce système consiste à combiner deux articulations apparentes, premièrement une tête métallique dans un insert de polyéthylène, articulé lui- même dans la concavité d'une cupule métallique fixée au bassin. En tant que tel, ce système biomécanique réduirait en théorie le risque de luxation. Dès lors, on aperçoit depuis environ 15 ans une augmentation progressive de l'utilisation de ce type d'implants que ce soit comme implant primaire ou secondaire, chez des patients jeunes ou âgés. Cependant, des études in vitro, ont montré que des grandes surfaces de friction sont associées à une augmentation de l'usure du polyéthylène (8). En revanche, les données sur la cinématique et l'usure, in vivo, de ce type d'implant étaient jusqu'alors limitées. Depuis quelques années, un certain nombre d'études cliniques avec un follow up significatif ont été publiées. CONCLUSIONS ET PERSPECTIVES FUTURES La prothèse totale de hanche à double mobilité, développée par Bousquet dans les années 1970, est un concept novateur dans l'arthroplastie totale de hanche. Depuis sa première conception, de nombreuses améliorations ont été adoptées. Cependant, ses effets à long terme sur la survie de l'implant doivent encore être effectué. Certes, des études ont montré un net effet sur la réduction du taux de luxation des prothèses primaires, lors de révision ou après résection tumorale. Toutefois, compte tenu des données limitées à long terme sur le taux d'usure et le descellement aseptique, il convient d'utiliser ce type d'implant avec prudence, en particulier lors d'arthroplastie primaire chez des patients jeunes.

Can resistance to trastuzumab be reversed by endocrine therapy? Combination of trastuzumab and letrozole after resistance to sequential trastuzumab and aromatase inhibitor monotherapies in patients with ER-positive, HER-2 positive, advanced breast cancer: a proof-of-concept trial (SAKK 23/03)

Introduction: Trastuzumab (T) is a cornerstone in the treatment of patients with HER2-overexpressing advanced breast cancer and development of resistance to T is a major therapeutic problem. HER-2 is part of a highly interactive signaling network that may impair efficacy of endocrine therapy. A sequential treatment design was chosen in this trial to ensure complete resistance to single agent therapy before receiving both a non-steroidal aromatase inhibitor (AI) and T. Any kind of clinical activity with combined treatment of AI and T after progression of single agent treatments could indicate restoration of sensitivity as a consequence of cross-talking and networking between both pathways. Methods: Key eligibility criteria included postmenopausal patients (pts.) with advanced, measurable, HER-2 positive (assessed by FISH, ratio (≥2)), HR positive disease and progression on prior treatment with a non-steroidal AI, e.g. letrozole or anastrozole, either in an adjuvant or advanced setting. Pts. received standard dose T monotherapy either weekly or three-weekly in step 1 and upon disease progression, continued T in combination with letrozole in step 2. The primary endpoint was clinical benefit response (CBR: CR, PR or SD for at least 24 weeks (+/- 1 week) according to RECIST) in step 2. Results: Thirteen pts. were enrolled in five centers in Switzerland. In step 1, six pts. (46%) achieved CBR. Median time to progression (TTP) was 161 days (Range: 50 - 627). Based on data collected until the end of May 2010, CBR was observed in seven out of the eleven evaluable pts. (64%) in step 2, including one pt. with partial response. Four of the seven pts. within step 2 that achieved CBR also had CBR in step 1. Seven out of eleven pts. have documented tumor progression during step 2 treatment. Median TTP for all eleven pts. was 184 days (range 61 - 471). Mean time on study treatment (TTP in step 1 plus TTP in step 2) for pts. reaching step 2 was 380 days (range 174 - 864). Adverse events were generally mild. Conclusion: Results of this proof-of-principle trial suggest that complete resistance to both AI and T can be overcome in a proportion of pts. by combined treatment of AI and T, as all pts. served as their own control. Our results appear promising for a new treatment strategy which offers a chemotherapy-free and well-tolerated option for at least a subset of the pts. with HR positive, HER-2 positive breast cancer. Further trials will need to corroborate this finding.

The concept of temporal 'plus' epilepsy.

The concept of temporal 'plus' epilepsy (T+E) is not new, and a number of observations made by means of intracerebral electrodes have illustrated the complexity of neuronal circuits that involve the temporal lobe. The term T+E was used to unify and better individualize these specific forms of multilobar epilepsies, which are characterized by electroclinical features primarily suggestive of temporal lobe epilepsy, MRI findings that are either unremarkable or show signs of hippocampal sclerosis, and intracranial recordings which demonstrate that seizures arise from a complex epileptogenic network including a combination of brain regions located within the temporal lobe and over closed neighbouring structures such as the orbitofrontal cortex, the insulo-opercular region, and the temporo-parieto-occipital junction. We will review here how the term of T+E has emerged, what it means, and which practical consideration it raises.

Modern Gamma Knife radiosurgery of vestibular schwannomas: treatment concept, volumetric tumor response, and functional results.

The objective of the present study was longitudinal evaluation of the volumetric tumor response and functional results after Gamma Knife radiosurgery of vestibular schwannomas, performed according to the modern standards of treatment. From October 2003 to September 2007, 133 consecutive patients with vestibular schwannomas were treated according to the concept of robotic Gamma Knife microradiosurgery, which is based on precise irradiation of the lesion, sparing adjacent structures, and delivery of the high radiation energy to the target. Multiple small-sized isocenters located within the border of the neoplasm were applied. The mean marginal dose was 11.5 Gy (range, 11-12 Gy). In total, 126 cases with a minimum posttreatment follow-up of 2 years (range, 2-7 years; median, 4 years) were analyzed. Temporary enlargement was noted in 25 % of tumors at 6 months after radiosurgery. At 3 years of follow-up, tumor shrinkage, stabilization, and increase in volume were marked in 73 %, 23 %, and 4 % of cases, respectively. All progressing lesions spontaneously stabilized later on and did not require additional management. In 3 % of patients, transitory impairment of the facial nerve function was marked; however, neither its permanent dysfunction nor trigeminal neuropathy attributed to radiosurgery was noted. Impairment of hearing compared to its pretreatment level was revealed in 4 %, 12 %, 13 %, and 16 % of patients at 6 months, 1 year, 2 years, and 3 years after radiosurgery, respectively, and this trend was statistically significant (P = 0.0042). Overall, 77 % of patients with serviceable hearing before treatment preserved it 3 years thereafter. In conclusion, modern Gamma Knife radiosurgery provides effective and safe management of vestibular schwannomas. Nevertheless, possible temporary tumor enlargement, delay of its growth arrest, transient dysfunction of the cranial nerves, and gradual deterioration of hearing after irradiation should be always taken into consideration.