Neuronal circuits within the homing pigeon hippocampal formation.

The current study aimed to reveal in detail patterns of intrahippocampal connectivity in homing pigeons (Columba livia). In light of recent physiological evidence suggesting differences between dorsomedial and ventrolateral hippocampal regions and a hitherto unknown laminar organization along the transverse axis, we also aimed to gain a higher-resolution understanding of the proposed pathway segregation. Both in vivo and high-resolution in vitro tracing techniques were employed and revealed a complex connectivity pattern along the subdivisions of the avian hippocampus. We uncovered connectivity pathways along the transverse axis that started in the dorsolateral hippocampus and continued to the dorsomedial subdivision, from where information was relayed to the triangular region either directly or indirectly via the V-shaped layers. The often-reciprocal connectivity along these subdivisions displayed an intriguing topographical arrangement such that two parallel pathways could be discerned along the ventrolateral (deep) and dorsomedial (superficial) aspects of the avian hippocampus. The segregation along the transverse axis was further supported by expression patterns of the glial fibrillary acidic protein and calbindin. Moreover, we found strong expression of Ca2+ /calmodulin-dependent kinase IIα and doublecortin in the lateral but not medial V-shape layer, indicating a difference between the two V-shaped layers. Overall, our findings provide an unprecedented, detailed description of avian intrahippocampal pathway connectivity, and confirm the recently proposed segregation of the avian hippocampus along the transverse axis. We also provide further support for the hypothesized homology of the lateral V-shape layer and the dorsomedial hippocampus with the dentate gyrus and Ammon's horn of mammals, respectively.

Mirror-induced behavior in the magpie (Pica pica): evidence of self-recognition.

Comparative studies suggest that at least some bird species have evolved mental skills similar to those found in humans and apes. This is indicated by feats such as tool use, episodic-like memory, and the ability to use one's own experience in predicting the behavior of conspecifics. It is, however, not yet clear whether these skills are accompanied by an understanding of the self. In apes, self-directed behavior in response to a mirror has been taken as evidence of self-recognition. We investigated mirror-induced behavior in the magpie, a songbird species from the crow family. As in apes, some individuals behaved in front of the mirror as if they were testing behavioral contingencies. When provided with a mark, magpies showed spontaneous mark-directed behavior. Our findings provide the first evidence of mirror self-recognition in a non-mammalian species. They suggest that essential components of human self-recognition have evolved independently in different vertebrate classes with a separate evolutionary history.

Visual responses and afferent connections of the n. ventrolateralis thalami (VLT) in the pigeon (Columba livia).

The nucleus ventrolateralis thalami (VLT) in pigeons receives direct retinal and forebrain projections and has reciprocal connections with the optic tectum. Although VLT is a component of the avian visual system, no study directly examined its connections or its cellular response characteristics. We, therefore, recorded from single units in the pigeon's VLT while visually stimulating the ipsi- and/or contralateral eye. In addition, tracing experiments were conducted to investigate its afferent connections. Electrophysiologically, we discovered three types of neurons, two of which were probably activated via a top-down telencephalotectal system (latencies > 100 ms). Type I neurons responded to uni- and bilateral and type II neurons exclusively to bilateral stimulation. Type III neurons were probably activated by retinal or retinotectal input (latencies < 27 ms) and responded to contra- and bilateral stimulation. Retrograde tracer injections into the VLT revealed an ipsilateral forebrain input from the visual Wulst, from subregions of the arcopallium, and bilateral afferents from the optic tectum. Most intriguing was the direct connection between the VLTs of both hemispheres. We suggest that the avian VLT is part of a system that integrates visuomotor processes which are controlled by both forebrain hemispheres and that VLT contributes to descending tectomotor mechanisms.