Collision-sensitive neurons in the optic tectum of the bullfrog, Rana catesbeiana

In this study, we examined the neuronal correlates of frog collision avoidance behavior. Single unit recordings in the optic tectum showed that 11 neurons gave selective responses to objects approaching on a direct collision course. The collision-sensitive neurons exhibited extremely tight tuning for collision bound trajectories with mean half-width at half height values of 0.8 and 0.9° (n = 4) for horizontal and vertical deviations, respectively. The response of frog collision-sensitive neurons can be fitted by a function that simply multiplies the size dependence of its response, e(-αθ(t)), by the image\u27s instantaneous angular velocity θ\u27(t). Using fitting analysis, we showed that the peak firing rate always occurred after the approaching object had reached a constant visual angle of 24.2 ± 2.6° (mean ± SD; n = 8), regardless of the approaching velocity. Moreover, a linear relationship was demonstrated between parameters l/v (l: object\u27s half-size, v: approach velocity) and time-to-collision (time difference between peak neuronal activity and the predicted collision) in the 11 collision-sensitive neurons. In addition, linear regression analysis was used to show that peak firing rate always occurred after the object had reached a constant angular size of 21.1° on the retina. The angular thresholds revealed by both theoretical analyses were comparable and showed a good agreement with that revealed by our previous behavioral experiments. This strongly suggests that the collision-sensitive neurons of the frog comprise a threshold detector, which triggers collision avoidance behavior

Cognitive Control of Escape Behaviour

When faced with potential predators, animals instinctively decide whether there is a threat they should escape from, and also when, how, and where to take evasive action. While escape is often viewed in classical ethology as an action that is released upon presentation of specific stimuli, successful and adaptive escape behaviour relies on integrating information from sensory systems, stored knowledge, and internal states. From a neuroscience perspective, escape is an incredibly rich model that provides opportunities for investigating processes such as perceptual and value-based decision-making, or action selection, in an ethological setting. We review recent research from laboratory and field studies that explore, at the behavioural and mechanistic levels, how elements from multiple information streams are integrated to generate flexible escape behaviour

A Novel Interception Strategy in a Miniature Robber Fly with Extreme Visual Acuity

Our visual system allows us to rapidly identify and intercept a moving object. When this object is far away, we base the trajectory on the target's location relative to an external frame of reference [1]. This process forms the basis for the constant bearing angle (CBA) model, a reactive strategy that ensures interception since the bearing angle, formed between the line joining pursuer and target (called the range vector) and an external reference line, is held constant [2-4]. The CBA model may be a fundamental and widespread strategy, as it is also known to explain the interception trajectories of bats and fish [5, 6]. Here, we show that the aerial attack of the tiny robber fly Holcocephala fusca is consistent with the CBA model. In addition, Holcocephala fusca displays a novel proactive strategy, termed "lock-on" phase, embedded with the later part of the flight. We found the object detection threshold for this species to be 0.13°, enabled by an extremely specialized, forward pointing fovea (∼5 ommatidia wide, interommatidial angle Δφ = 0.28°, photoreceptor acceptance angle Δρ = 0.27°). This study furthers our understanding of the accurate performance that a miniature brain can achieve in highly demanding sensorimotor tasks and suggests the presence of equivalent mechanisms for target interception across a wide range of taxa.This work was funded by the Air Force Office of Scientific Research (FA9550-15-1-0188 to P.T.G.-B. and K.N. and FA9550-15-1-0068 to D.G.S.), an Isaac Newton Trust/Wellcome Trust ISSF/University of Cambridge Joint Research Grant (097814/Z/11/Z) to P.T.G.-B., a Biotechnology and Biological Sciences Research Council David Phillips Fellowship (BBSRC, BB/L024667/1) to T.J.W., a Royal Society International Exchange Scheme grant to P.T.G.-B. (75166), a Swedish Research Council grant (2012-4740) to K.N., and a Shared Equipment Grant from the School of Biological Sciences (University of Cambridge, RG70368)

Exploring behavioral circuits with holographic optogenetics and network imaging

Included works This thesis contains three previously published works: Semmelhack, Donovan, et al.; eLife 2014 Temizer, Donovan, et al.; Current Biology 2015 Thiele, Donovan, Baier; Neuron 2014 And one full manuscript, soon to be in the second round of review: Dal Maschio*, Donovan*, et al. *(Equal contributions) The work presented in these manuscripts is equivalent to a standard thesis

Collision avoidance behaviour in a pair of flying locusts (Locusta migratoria L.)

Migratory locusts; Locusta migratoria L. flying in a swarm would encounter spatiotemporally complex visual cues such as translating, receding and looming stimuli, produced by self-motion as well as object motion in the environment. A rapidly approaching conspecific or a predator represents a looming object approaching on a collision course and is involved in triggering urgent collision avoidance behaviours. To avoid predators and collision with conspecifics, and to navigate through complex environments, locusts must produce appropriate collision avoidance manoeuvres. Flying locusts have evolved the ability to not only avoid predation but also effectively navigate within the swarm without constantly colliding with one another. Collision avoidance and predator evasion in response to looming stimuli are important in many animals and in locusts, the key elements in the neuronal pathway underlying this behaviour are the lobula giant movement detector (LGMD) and its postsynaptic component, the descending contralateral movement detector (DCMD). Previous studies have suggested that the LGMD/DCMD pathway allows each locust within a dense swarm to remain sensitive to approaches of individual objects including conspecifics and flying predators, approaching frequently from many directions or along the same trajectory and to produce appropriate collision avoidance behaviours. Collision avoidance responses of a rigidly tethered locust presented with a looming object have been studied previously. However, behavioural strategies for collision avoidance within a group of conspecifics are yet unknown. Avoidance behaviour exhibited by a single locust may or may not differ from that of an individual in a group. Further, salient cues produced by objects on a collision course (looming) can be influenced by each animal’s position relative to the object and/or its position within a group. In my first objective of this thesis, I exposed locusts (L. migratoria L.) to a computer generated looming object in the presence of a live and dead conspecific separately. This first experiment was done to determine if collision avoidance behaviour of a locust: Locust 1 (L1) or Locust 2 (L2), is affected by the presence of a conspecific. As my second objective, the responses of a pair of flying locusts placed in differing relative positions in a wind tunnel were studied during presentation of the same looming object. This second experiment was done to determine if collision avoidance behaviour of a locust is affected by the relative position of a conspecific. From the results, I looked at different spatio-temporal characteristics of L1 and L2 collision avoidance behaviour and their dependency on the presence as well as on different relative positions of a conspecific in the vicinity. Results from Experiment 1 showed that the types of collision avoidance responses, some components of six degrees of freedom of L1 and L2 and also the timing of the onset and duration of the initial avoidance response of L2, were affected by the presence of a conspecific. According to Experiment 2, the avoidance responses and three translational degrees of freedom of L1 and L2 were also affected by the relative position of the conspecific and its own position, respectively. Also, I found that the timing of the onset and the duration of the initial avoidance response of L2 were affected by its own position in the wind tunnel. Both locusts’ responses to the looming stimuli were more robust in the presence of a live conspecific and less pronounced in the presence of a dead locust. Thus, results further suggest that locusts use visual cues from the looming objects as well as an immediate conspecific to generate appropriate avoidance responses. Taken together, the results of my study indicate that a locust’s collision avoidance behaviour can be affected by the presence as well as the relative position of a conspecific in the vicinity

Sensory coding in an identified motion-sensitive visual neuron of the locust (Locusta migratoria)

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). Previous studies have suggested that this pathway is also affected by more complicated movements in the locust’s 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. 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 locust’s 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. Taken together, these results illustrate that the encoding of visual stimuli in single neurons is dynamic and likely much more complicated than previously thought

Cognitive Control of Escape Behaviour

When faced with potential predators, animals instinctively decide whether there is a threat they should escape from, and also when, how, and where to take evasive action. While escape is often viewed in classical ethology as an action that is released upon presentation of specific stimuli, successful and adaptive escape behaviour relies on integrating information from sensory systems, stored knowledge, and internal states. From a neuroscience perspective, escape is an incredibly rich model that provides opportunities for investigating processes such as perceptual and value-based decision-making, or action selection, in an ethological setting. We review recent research from laboratory and field studies that explore, at the behavioural and mechanistic levels, how elements from multiple information streams are integrated to generate flexible escape behaviour

Spatial-memory control of defensive actions

Adapting anti-predatory defensive strategies to the properties of the environment is critical for survival. Here, I investigated the dependence of mouse instinctive defensive behaviours on memory of the spatial environment, and the neural mechanisms responsible for accurate escape towards refuge. First, using behavioural assays, I show that the choice and execution of defensive behaviours rely on rapidly acquired memory and are promptly updated following acute changes in the environment. In the presence of a known refuge mice escape directly to it, even if this requires approaching the source of threat. Escape is initiated by a memory- guided, accurate head-rotation movement towards the location of the refuge, indicating knowledge of the spatial goal prior to flight start. Second, I demonstrate that the superior colliculus (SC) is essential to accurately orient to shelter during escape, in agreement with its known role in both sensory- and memory- guided head orientation. To identify which upstream areas provide information about refuge location to the SC, I retrogradely traced the SC afferents and performed loss-of- function experiments in candidate areas, which showed that the retrosplenial cortex (RSC) plays a critical role in escape accuracy. Furthermore, channelrhodopsin-2-assisted connectivity studies showed a functional connection between RSC and SC, and chemogenetic inactivation of this projection impaired accurate orientation to refuge during escape. To understand how the RSC and SC control orientation to shelter during escape, I performed simultaneous single-unit recordings from the RSC and SC with Neuropixels probes. Both RSC and SC were found to encode the angular offset between the mouse’s heading and the shelter, at the single-neuron and population levels. Chemogenetic inactivation of SC-projecting RSC neurons disrupts encoding of head-shelter offset in both regions, but it does not compromise the SC motor function during a sensory- orientation task. In summary, I show that escape is a flexible behaviour and its accuracy critically depends on a monosynaptic projection from the RSC to SC. In addition, I show RSC-dependent egocentric encoding of goal direction at SC, an area critical for orientation during escape, providing a possible mechanism for controlling ethologically relevant goal-directed navigation.Boehringer Ingelheim Fellowshi

Neuronal circuits underlying visual attention during naturalistic behaviour in zebrafish larvae

To survive, animals need to sustain behavioural responses towards specific environmental stimuli to achieve an overall goal. One example is the hunting behaviour of zebrafish larvae, which is characterised by a set of discrete visuomotor events that begin with prey detection, followed by target-directed swims and end with prey capture. Several studies have begun elucidating the neuronal circuits that govern prey detection and initiation of hunting routines, which are largely dependent on the midbrain optic tectum (OT). However, it is not known how the brain is able to sustain a behavioural routine directed towards a specific target, especially in complex environments containing distractors. In this study, I have discovered that the nucleus isthmus (NI), a midbrain nucleus implicated in visual attention in other vertebrates, is required for sustained tracking of prey during hunting routines in zebrafish larvae. NI neurons co-express cholinergic and glutamatergic markers and possess two types of axonal projection morphology. The first type targets the ipsilateral OT and AF7, a retinorecipient pretectal region involved in hunting. The second type projects bilaterally to the deep OT layers. Laser ablation of the NI followed by tracking of naturalistic hunting behaviour, revealed that while hunting initiation rates and motor kinematics were unaltered, ablated animals showed an elevated probability of aborting hunting routines midway. Moreover, 2-photon calcium imaging of tethered larvae during a closed-loop virtual reality hunting assay, showed that NI neurons are specifically active during hunting. These results suggest that the NI supports the maintenance of action sequences towards specific prey targets during hunting, most likely by modulating pretectal and tectal activity. This in turn supports its presence at the centre of an evolutionarily conserved circuit to control selective attention to ethologically relevant stimuli in the presence of competing distractors