Vertical Lobes of the Mushroom Bodies Are Essential for View-Based Navigation in Australian Myrmecia Ants

Abstract

Prior to leaving home, insects acquire visual landmark information through a series of well-choreographed walks or flights of learning [1-4]. This information allows them to pinpoint goals both when in their vicinity [5-7] and from locations they have not previously visited [8-10]. It is presumed that animals returning home match memorized views to their current view for successful view-based navigation [11]. While view-based navigation strategies have been incorporated into several navigation models [8, 12, 13], we still know little about how this behavior is performed by the insect brain. Mushroom bodies are essential for visual learning and memory [14-16], and therefore we investigated their role in view-based navigation in a visually oriented ant, Myrmecia midas. We injected the local anesthetic procaine [15, 17, 18] into the mushroom body vertical lobes (VLs) to selectively inhibit neural activity in this region. We compared the behavior of VL-procaine-treated ants with three groups: untreated control, VL-saline, and off-target (antennal lobe) procaine. Experienced foragers were collected, treated, and released in their familiar environment where we documented their behavior. Animals with procaine-inactivated VLs had tortuous paths and were unable to find their nest, whereas ants from the untreated and off-target procaine groups were well directed and were the most successful at returning home. Untreated animals walked faster when their gaze was directed toward home, and this behavior was eliminated by anesthetizing the VL region. Our data provide neurobiological evidence that the mushroom body vertical lobes are necessary for retrieving visual memories for successful view-based navigation.