“Crow King” from a collection of corvid portraits owned by Dr. Kenneth M Beck
Science Journals — AAAS
Andreas Nieder*, Lysann Wagener, Paul Rinnert
Humans have tended to believe that we are the only species to possess certain traits, behaviors, or abilities, especially with regard to cognition. Occasionally, we extend such traits to primates or other mammals—species with which we share fundamental brain similarities. Over time, more and more of these supposed pillars of human exceptionalism have fallen. Nieder et al. now argue that the relationship between consciousness and a standard cerebral cortex is another fallen pillar (see the Perspective by Herculano-Houzel). Specifically, carrion crows show a neuronal response in the palliative end brain during the performance of a task that correlates with their perception of a stimulus. Such activity might be a broad marker for consciousness…”
“Subjective experiences that can be consciously accessed and reported are associated with the cerebral cortex. Whether sensory consciousness can also arise from differently organized brains that lack a layered cerebral cortex, such as the bird brain, remains unknown. We show that single-neuron responses in the pallial endbrain of crows performing a visual detection task correlate with the birds’ perception about stimulus presence or absence and argue that this is an empirical marker of avian consciousness. Neuronal activity follows a temporal two-stage process in which the first activity component mainly reflects physical stimulus intensity, whereas the later component predicts the crows’ perceptual reports. These results suggest that the neural foundations that allow sensory consciousness arose either before the emergence of mammals or independently in at least the avian lineage and do not necessarily require a cerebral cortex.
“Sensory consciousness, the ability to have subjective experience that can be explicitly accessed and thus reported, arises from brain processes that emerged through evolutionary history (1, 2). Today, the neural correlates of consciousness are primarily associated with the workings of the primate cerebral cortex (3–6), a part of the telencephalic pallium that is laminar in organization (7–9). Birds, by contrast, have evolved a different pallium since they diverged from the mammalian lineage 320 million years ago (10, 11). The bird pallium retains organizational principles reminiscent of the mammalian brain (12) but is distinctively nuclear and lacks a layered cerebral cortex (13–15). Despite this, birds demonstrate sophisticated perceptual and cognitive behaviors that suggest conscious experiences (16, 17).
“The associative endbrain area called nidopallium caudolaterale (NCL) is linked to high-level cognition in birds (18, 19) and is considered a putative avian analog of the mammalian prefrontal cortex (20), which plays a predominant role in sensory consciousness in primates (21–23). To signify a “neural correlate of consciousness” in primates, brain activity that systematically changes with the subject’s report of whether or not it had perceived identical stimuli is identified (24, 25). We hypothesized that conscious experience originates from activity of the NCL in corvids and used a corresponding experimental protocol in which only the crows’ internal state, not the physical stimulus properties, determined their subjective experience.
“We trained two carrion crows (Corvus corone) to report the presence or absence of visual stimuli around perceptual threshold in a rule-based delayed detection task (Fig. 1A and supplementary materials and methods). At perceptual threshold, the internal state of the crows determined whether stimuli of identical intensity would be seen or not perceived. After a delay, a rule cue informed the crow about which motor action was required to report its percept. Thus, the crows could not prepare motor responses prior to the rule cues, which enabled the investigation of neuronal activity related to subjective sensory experience and its lasting accessibility…”
BELOW IS A LINK TO THE FULL ARTICLE PDF FROM SCIENCE, the magazine of the American Association for The Advancement of Science.