EEG responses to visual landmarks in flying pigeons.

BACKGROUND: GPS analysis of flight trajectories of pigeons can reveal that topographic features influence their flight paths. Recording electrical brain activity that reflects attentional processing could indicate objects of interest that do not cause changes in the flight path. Therefore, we investigated whether crossing particular visual landmarks when homing from a familiar release site is associated with changes in EEG. RESULTS: Birds carried both data-loggers for recording GPS position and EEG during flight. First, we classified characteristic EEG frequencies of caged birds and found five main bands: A: 0-3, B: 3-12, C: 12-60, D: 60-130, and E: 130-200 Hz. We analyzed changes in these activity bands when pigeons were released over sea (a featureless environment) and over land. Passing over the coastline and other prominent landmarks produced a pattern of EEG alterations consisting of two phases: activation of EEG in the high-frequency bands (D and/or E), followed by activation of C. Overlaying the EEG activity with GPS tracks allowed us to identify topographical features of interest for the pigeons that were not recognizable by distinct changes of their flight path. CONCLUSIONS: We provide evidence that EEG analysis can identify landmarks and objects of interest during homing. Middle-frequency activity (C) reflects visual perception of prominent landmarks, whereas activation of higher frequencies (D and E) is linked with information processing at a higher level. Activation of E bands is likely to reflect an initial process of orientation and is not necessarily linked with processing of visual information.

Miniature neurologgers for flying pigeons: multichannel EEG and action and field potentials in combination with GPS recording.

To study the neurophysiology of large-scale spatial cognition, we analyzed the neuronal activity of navigating homing pigeons. This is not possible using conventional radio-telemetry suitable for short distances only. Therefore we developed a miniaturized data logger ("neurologger") that can be carried by a homing pigeon on its back, in conjunction with a micro-global position system (GPS) logger recording the spatial position of the bird. In its present state, the neurologger permits recording from up to eight single-ended or differential electrodes in a walking or flying pigeon. Inputs from eight independent channels are preamplified, band-pass filtered, and directed to an eight-channel, 10-bit analog-digital converter of the microcontroller storing data on a "Multimedia" or "Secure Digital" card. For electroencephalography (EEG), the logger permits simultaneous recordings of up to eight channels during maximally 47 h, depending on memory, while single unit activity from two channels can be stored over 9 h. The logger permits single unit separation from recorded multiunit signals. The neurologger with GPS represents a better alternative to telemetry that will eventually permit to record neuronal activity during cognitive and innate behavior of many species moving freely in their habitats but will also permit automated high-throughput screening of EEG in the laboratory.