Visual environments may contain a complex combination of object motion. Animals respond to features of complexity by generating adaptive behavioural responses. One important feature of a complex visual environment is a rapidly expanding object in the visual field (looming) which may represent an approaching predator or an object on a collision path. Many animals respond to looming objects by generating avoidance behaviours (Maier et al. 2004; Santer et al. 2005; Oliva et al. 2007) and neurons involved in the detection and relay of looming stimuli are present in birds (Sun and Frost 1998) and many insects (Simmons and Rind 1992; Hatsopoulos et al. 1995; Wicklein and Strausfeld 2000). One of the most widely studied visual pathways is found in the locust. This visual pathway, which includes the lobula giant motion detector (LGMD) and its post-synaptic target, the descending contralateral motion detector (DCMD), signals the approach a looming visual stimulus (Schlotterer, 1977; Simmons and Rind, 1992; Hatsopoulos et al., 1995). The DCMD descends through the ventral nerve cord and synapses with motorneurons involved in predator evasion and collision avoidance (Simmons, 1980; Simmons and Rind, 1992; Santer et al., 2006).<p> Previous studies have suggested that this pathway is also affected by more complicated movements in the locusts visual environment. For example, Guest and Gray (2006) demonstrated that the approach of paired objects in the azimuthal position and approaches at different time intervals affect DCMD firing rate properties. In my first objective of this thesis (Chapter 2), I tested locusts with computer-generated discs that traveled along a combination of non-colliding (translating) and colliding (looming) trajectories and demonstrate how distinctly different DCMD responses result from different trajectory types. In addition to estimating the time of collision and direction of object travel, the presence of a discernable peak associated with the time of object deviation suggests that DCMD responses may contain information related to changes in motion.<p> Previous studies suggest that LGMD/DCMD encodes approaching objects using rate coding; edge expansion of approaching objects causes an increased rate of neuronal firing (Schlotterer, 1977; Hatsopoulos et al., 1995; Judge and Rind, 1997; Gabbiani et al., 1999). Based on observations of DCMD responses to simple looming objects that showed oscillations in DCMD responses (for example, Fig. 1D Santer et al., 2006) and the fact that bursting occurs in many other sensory systems (Yu and Margoliash, 1996; Sherman, 2001; Krahe and Gabbiani, 2004; Marsat and Pollack, 2006), it was hypothesized that the DCMD may show bursting activity. In my second objective of this thesis (Chapter 3), I tested locusts with simple looming stimuli known to generate behavioural responses in order to identify and quantify bursting activity. Results show that the highest frequency of bursts occurred at intervals of 40-50 ms (20-25 Hz). The behavioural significance of this frequency is related to the average wingbeat frequency of the locusts forewing during flight (~25 Hz; Robertson and Johnson, 1993). Based on previous evidence of DCMD flight-gating (see, for example, Santer et al., 2006), bursting may gate information into the flight circuitry, thereby providing visual feedback that may be modified to generate an avoidance response during flight. Single spiking and bursting occurred throughout object approach up until the late stage of approach, where burst frequency rapidly increased. Results predict that the DMCD may use a bimodal coding strategy to detect looming visual stimuli, where single spiking at the beginning of approach may result in subtle course changes during flight and bursting near the time of collision may initiate an evasive glide.<p> Taken together, these results illustrate that the encoding of visual stimuli in single neurons is dynamic and likely much more complicated than previously thought.

Visual environments may contain a complex combination of object motion. Animals respond to features of complexity by generating adaptive behavioural responses. One important feature of a complex visual environment is a rapidly expanding object in the visual field (looming) which may represent an approaching predator or an object on a collision path. Many animals respond to looming objects by generating avoidance behaviours (Maier et al. 2004; Santer et al. 2005; Oliva et al. 2007) and neurons involved in the detection and relay of looming stimuli are present in birds (Sun and Frost 1998) and many insects (Simmons and Rind 1992; Hatsopoulos et al. 1995; Wicklein and Strausfeld 2000). One of the most widely studied visual pathways is found in the locust. This visual pathway, which includes the lobula giant motion detector (LGMD) and its post-synaptic target, the descending contralateral motion detector (DCMD), signals the approach a looming visual stimulus (Schlotterer, 1977; Simmons and Rind, 1992; Hatsopoulos et al., 1995). The DCMD descends through the ventral nerve cord and synapses with motorneurons involved in predator evasion and collision avoidance (Simmons, 1980; Simmons and Rind, 1992; Santer et al., 2006).<p> Previous studies have suggested that this pathway is also affected by more complicated movements in the locusts visual environment. For example, Guest and Gray (2006) demonstrated that the approach of paired objects in the azimuthal position and approaches at different time intervals affect DCMD firing rate properties. In my first objective of this thesis (Chapter 2), I tested locusts with computer-generated discs that traveled along a combination of non-colliding (translating) and colliding (looming) trajectories and demonstrate how distinctly different DCMD responses result from different trajectory types. In addition to estimating the time of collision and direction of object travel, the presence of a discernable peak associated with the time of object deviation suggests that DCMD responses may contain information related to changes in motion.<p> Previous studies suggest that LGMD/DCMD encodes approaching objects using rate coding; edge expansion of approaching objects causes an increased rate of neuronal firing (Schlotterer, 1977; Hatsopoulos et al., 1995; Judge and Rind, 1997; Gabbiani et al., 1999). Based on observations of DCMD responses to simple looming objects that showed oscillations in DCMD responses (for example, Fig. 1D Santer et al., 2006) and the fact that bursting occurs in many other sensory systems (Yu and Margoliash, 1996; Sherman, 2001; Krahe and Gabbiani, 2004; Marsat and Pollack, 2006), it was hypothesized that the DCMD may show bursting activity. In my second objective of this thesis (Chapter 3), I tested locusts with simple looming stimuli known to generate behavioural responses in order to identify and quantify bursting activity. Results show that the highest frequency of bursts occurred at intervals of 40-50 ms (20-25 Hz). The behavioural significance of this frequency is related to the average wingbeat frequency of the locusts forewing during flight (~25 Hz; Robertson and Johnson, 1993). Based on previous evidence of DCMD flight-gating (see, for example, Santer et al., 2006), bursting may gate information into the flight circuitry, thereby providing visual feedback that may be modified to generate an avoidance response during flight. Single spiking and bursting occurred throughout object approach up until the late stage of approach, where burst frequency rapidly increased. Results predict that the DMCD may use a bimodal coding strategy to detect looming visual stimuli, where single spiking at the beginning of approach may result in subtle course changes during flight and bursting near the time of collision may initiate an evasive glide.<p> Taken together, these results illustrate that the encoding of visual stimuli in single neurons is dynamic and likely much more complicated than previously thought.

Odors that are essential to the survival and reproduction of a species take the form of complex mixtures of volatiles. Often, an odor source such as food or a potential mate releases a mixture with characteristic ratios between the components. Here, the encoding of the characteristic ratio between components of the pheromone released by a female moth is investigated in the antennal lobe (AL) of a male moth (Manduca sexta). The mechanisms by which olfactory systems of diverse insect species process odors are adapted to the particular environment and olfactory behavior of the animal. In the moth, innately attractive odors produce patterns of synchrony in the output of the AL, the projection neurons (PNs). Male moths exhibited attraction to synthetic mixtures of pheromone components that was selective for ratios at or near the natural ratio released by females. Selectivity increased as the moth neared the odor source and initiated mating behaviors. PNs in the macroglomerular complex (MGC) did not exhibit an effect of component ratio on their firing rate responses. However, pairs of PNs exhibited increased synchrony in response to the behaviorally effective ratios of pheromone components. Individual pairs exhibited selectivity for ratios within 1 order of magnitude from the natural ratio. Synchrony in PN spiking was not phase-locked to the network oscillations in the AL. A model for ratio-selective enhancement of synchronous PN output in the AL is proposed.

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<p>The ability to monitor, learn from, and respond to social information is essential for many highly social animals, including humans. Deficits to this capacity are associated with numerous psychopathologies, including autism spectrum disorders, social anxiety disorder, and schizophrenia. To understand the neural mechanisms supporting social information seeking behavior requires understanding this behavior in its natural context, and presenting animals with species-appropriate stimuli that will elicit the behavior in the laboratory. In this dissertation, I describe a novel behavioral paradigm I developed for investigating social information seeking behavior in rhesus macaques in a laboratory setting, with the use of naturalistic videos of freely-behaving conspecifics as stimuli. I recorded neural activity in the orbitofrontal and lateral prefrontal cortex of monkeys as they engaged in this task, and found evidence for a rich but sparse representation of natural behaviors in both areas, particularly in the orbitofrontal cortex. This sparse encoding of conspecifics' behaviors represents the raw material for social information foraging decisions.</p> / Dissertation

Behavioural phonotaxis (oriented movement in response to sound) is an effective means to quantify auditory perception in acoustically communicating insects. Previous phonotaxis studies on the acoustic parasitoid fly Ormia ochracea (Diptera: Tachinidae) have described stereotyped, reflex-like responses towards auditory stimuli modeled after their preferred cricket hosts, yet their ability to demonstrate plasticity of responses in the context of dynamically changing auditory cues has not previously been described. Using a behavioural sensitization protocol, I compared phonotaxis towards behaviourally irrelevant (non-attractive) test stimuli presented alone, and when preceded with the natural, response-evoking cricket song (attractive). Results demonstrate the cricket song as a sensitizing stimulus mediating phonotaxis towards otherwise non-attractive sounds, and differential walking patterns depending on temporal delay between song offset and test stimulus onset. My findings suggest an ecological purpose of sensitization, allowing flies to maintain orientation towards a cricket host amidst conditions of signal disruption in the environment.

Behavioural phonotaxis (oriented movement in response to sound) is an effective means to quantify auditory perception in acoustically communicating insects. Previous phonotaxis studies on the acoustic parasitoid fly Ormia ochracea (Diptera: Tachinidae) have described stereotyped, reflex-like responses towards auditory stimuli modeled after their preferred cricket hosts, yet their ability to demonstrate plasticity of responses in the context of dynamically changing auditory cues has not previously been described. Using a behavioural sensitization protocol, I compared phonotaxis towards behaviourally irrelevant (non-attractive) test stimuli presented alone, and when preceded with the natural, response-evoking cricket song (attractive). Results demonstrate the cricket song as a sensitizing stimulus mediating phonotaxis towards otherwise non-attractive sounds, and differential walking patterns depending on temporal delay between song offset and test stimulus onset. My findings suggest an ecological purpose of sensitization, allowing flies to maintain orientation towards a cricket host amidst conditions of signal disruption in the environment.

abstract: Food is an essential driver of animal behavior. For social organisms, the acquisition of food guides interactions with the environment and with group-mates. Studies have focused on how social individuals find and choose food sources, and share both food and information with group-mates. However, it is often not clear how experiences throughout an individual's life influence such interactions. The core question of this thesis is how individuals’ experience contributes to within-caste behavioral variation in a social group. I investigate the effects of individual history, including physical injury and food-related experience, on individuals' social food sharing behavior, responses to food-related stimuli, and the associated neural biogenic amine signaling pathways. I use the eusocial honey bee (Apis mellifera) system, one in which individuals exhibit a high degree of plasticity in responses to environmental stimuli and there is a richness of communicatory pathways for food-related information. Foraging exposes honey bees to aversive experiences such as predation, con-specific competition, and environmental toxins. I show that foraging experience changes individuals' response thresholds to sucrose, a main component of adults’ diets, depending on whether foraging conditions are benign or aversive. Bodily injury is demonstrated to reduce individuals' appetitive responses to new, potentially food-predictive odors. Aversive conditions also impact an individual's social food sharing behavior; mouth-to-mouse trophallaxis with particular groupmates is modulated by aversive foraging conditions both for foragers who directly experienced these conditions and non-foragers who were influenced via social contact with foragers. Although the mechanisms underlying these behavioral changes have yet to be resolved, my results implicate biogenic amine signaling pathways as a potential component. Serotonin and octopamine concentrations are shown to undergo long-term change due to distinct foraging experiences. My work serves to highlight the malleability of a social individual's food-related behavior, suggesting that environmental conditions shape how individuals respond to food and share information with group-mates. This thesis contributes to a deeper understanding of inter-individual variation in animal behavior. / Dissertation/Thesis / Doctoral Dissertation Biology 2017

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