Several recent publications have highlighted the neural complexity and intelligence associated with the brains of birds. Many studies suggest that the neural seat of both working memory and executive control - which together encompass planning, creativity, reasoning, abstraction, and most of the other higher-order cognitive properties humans like to claim as their own - lies within the prefrontal cortex. In a new study, Jonas Rose and Michael Colombo investigate the neural basis of executive control in homing pigeons by recording from the nidopallium caudolaterale (NCL), a region of the avian brain considered analogous to the mammalian prefrontal cortex. They show that neurons in the NCL selectively fire when the birds are told to remember and stop firing when they are told to forget.
The authors trained five pigeons on a directed forgetting test, a variation on the classic match-to-sample test. After viewing sample stimuli consisting of one of two shapes (a circle or dot) or colors (red or white), the birds were cued to remember or forget the sample (signaled by either a high- or low-frequency tone or one of two distinct patterns). A delay period followed these cues. If a forget cue was presented, the trial ended after the delay, and no memory test was given. If the remember cue was presented, the birds were given a memory test in which they saw two stimuli after the delay; if they responded to the sample stimulus (by pecking on a key), they were rewarded with wheat.
Rose and Colombo found that during the remember trials only, neurons in the NCL showed sustained activation throughout the cue and delay periods; during the forget trials, sustained activation disappeared. These results suggest that sustained NCL neuronal activation reflects working memory or at least some type of cognitive activity associated with executive control. And though the avian NCL and mammalian prefrontal cortex clearly differ after 320 million years of divergent evolution, Rose and Colombo make a strong case that they are similar enough to support the NCL's likely contribution to executive control in mammals as well. And they suggest that seeing such similarities between the bird and human brain forces us to reexamine not only our notions of how these structures operate but also our hubris in thinking our biology and nature is unique.
Citation: Rose J, Colombo M (2005) Neural correlates of executive control in the avian brain. PLoS Biol 3(6): e190.
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