Showing papers by "Nicholas J. Strausfeld published in 2000"

Organization and significance of neurons that detect change of visual depth in the hawk moth Manduca sexta.

Abstract: Visual stimuli representing looming or receding objects can be decomposed into four parameters: change in luminance; increase or decrease of area; increase or decrease of object perimeter length; and motion of the object’s perimeter or edge. This paper describes intracellular recordings from visual neurons in the optic lobes of Manduca sexta that are selectively activated by certain of these parameters. Two classes of wide-field neurons have been identified that respond selectively to looming and receding stimuli. Class 1 cells respond to parameters of the image other than motion stimuli. They discriminate an approaching or receding disc from an outwardly or inwardly rotating spiral, being activated only by the disc and not by the spiral. Class 2 neurons respond to moving edges. They respond both to movement of the spiral and to an approaching or receding disc. These two classes are further subdivided into neurons that are excited by image expansion (looming) and are inhibited by image contraction (antilooming). Class 2 neurons also respond to horizontal and vertical movement of gratings over the retina. Stimulating class 1 and 2 neurons with white discs against a dark background results in the same activation as stimulation with dark discs against a white background, demonstrating that changes in luminance play no role in the detection of looming or antilooming. The present results show that the two types of looming-sensitive neurons in M. sexta use different mechanisms to detect the approach or retreat of an object. It is proposed that cardinal parameters for this are change of perimeter length detected by class 1 neurons and expansion or contraction visual flow fields detected by class 2 neurons. These two classes also differ with respect to their polarity, the former comprising centripetal cells from the optic lobes to the midbrain, the latter comprising centrifugal neurons from the midbrain to the optic lobes. The significance of these arrangements with respect to hovering flight is discussed. J. Comp. Neurol. 424:356‐376, 2000. © 2000 Wiley-Liss, Inc.

Parallel organization in honey bee mushroom bodies by peptidergic Kenyon cells.

Abstract: Antisera against the neuromodulatory peptides, Phe-Met-Arg-Phe-NH(2)-amide (FMRFamide) and gastrin cholecystokinin, demonstrate that the mushroom bodies of honey bees are subdivided longitudinally into strata. Three-dimensional reconstructions demonstrate that these strata project in parallel through the entire pedunculus and through the medial and vertical lobes. Immunostaining reveals clusters of immunoreactive cell bodies within the calyx cups and immunoreactive bundles of axons that line the inside of the calyx cup and lead to strata. Together, these features reveal that immunoreactive strata are composed of Kenyon cell axons rather than extrinsic elements, as suggested previously by some authors. Sorting amongst Kenyon cell axons into their appropriate strata already begins in the calyx before these axons enter the pedunculus. The three main concentric divisions of each calyx (the lip, collar, and basal ring) are divided further into immunoreactive and immunonegative zones. The lip neuropil is divided into two discrete zones, the collar neuropil is divided into five zones, and the basal ring neuropil is divided into four zones. Earlier studies proposed that the lip, collar, and basal ring are represented by three broad bands in the lobes: axons from adjacent Kenyon cell dendrites in the calyces are adjacent in the lobes even after their polar arrangements in the calyces have been transformed to rectilinear arrangements in the lobes. The universality of this arrangement is not supported by the present results. Although immunoreactive zones are found in all three calycal regions, immunoreactive strata in the lobes occur mainly in the two bands that were ascribed previously to the collar and the basal ring. In the lobes, immunoreactive strata are visited by the dendrites of efferent neurons that carry information from the mushroom bodies to other parts of the brain. Morphologically and chemically distinct subdivisions through the pedunculus and lobes of honey bees are comparable to longitudinal subdivisions demonstrated in the mushroom bodies of other insects, such as the cockroach Periplaneta americana. The functional and evolutionary significance of the results is discussed.

Exploitation of an Ancient Escape Circuit by an Avian Predator: Prey Sensitivity to Model Predator Display in the Field

Abstract: Certain insectivorous birds, such as the painted redstart (Myioborus pictus), undertake flush pursuit – a characteristic display that elicits an escape reaction by an insect, which

Optic flow representation in the optic lobes of Diptera: modeling innervation matrices onto collators and their evolutionary implications.

Abstract: A network model of optic flow processing, based on physiological and anatomical features of motion-processing neurons, is used to investigate the role of small-field motion detectors emulating T5 cells in producing optic flow selective properties in wide-field collator neurons. The imposition of different connectivities can mimic variations observed in comparative studies of lobula plate architecture across the Diptera. The results identify two features that are crucial for optic flow selectivity: the broadness of the spatial patterns of synaptic connections from motion detectors to collators, and the relative contributions of excitatory and inhibitory synaptic outputs. If these two aspects of the innervation matrix are balanced appropriately, the network's sensitivity to perturbations in physiological properties of the small-field motion detectors is dramatically reduced, suggesting that sensory systems can evolve robust mechanisms that do not rely upon precise control of network parameters. These results also suggest that alternative lobula plate architectures observed in insects are consistent in allowing optic flow selective properties in wide-field neurons. The implications for the evolution of optic flow selective neurons are discussed.

Optic flow representation in the optic lobes of Diptera: modeling the role of T5 directional tuning properties.

Abstract: An evolutionarily conserved system of small retinotopic neurons in dipteran insects, called bushy T-cells, provides information about directional motion to large collator neurons in the lobula plate. Physiological and anatomical features of these cells provide the basis for a model that is used to investigate requirements for generating optic flow selectivity in collators while allowing for evolutionary variations. This account focuses on the role of physiological tuning properties of T5 neurons. Various flow fields are defined as inputs to retinotopic arrays of T5 cells, the responses of which are mapped onto collators using innervation matrices that promote selectivity for flow type and position. Properties known or inferred from physiological and anatomical studies of neurons contributing to motion detection are incorporated into the model: broad tuning to local motion direction and the representation of each visual sampling unit by a quartet of small-field T5-like neurons with orthogonal preferred directions. The model predicts hitherto untested response properties of optic flow selective collators, and predicts that selectivity for a given flow field can be highly sensitive to perturbations in physiological properties of the motion detectors.