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In a serial-order task, subjects are trained to respond to five stimuli in a specific order, (e.g., A → B → C → D → E) to obtain a reward. Once the serial-order task is learned, a pairwise test is administered in which all ten pairwise combinations of the five stimuli are presented to the subject. Humans and monkeys respond at high levels on all pairwise items, that is, they respond to the items in the pair in the order in which they appear in the original sequence. Given pair BD, for example, humans and monkeys first respond to item B and then item D. Examination of the latencies reveals that humans and monkeys show a first-item effect, a missing-item effect, and a symbolic-distance effect, all in line with the view that they form a representation of the order of the five items and use that representation to guide their behaviour during the pairwise test. In contrast, pigeons perform poorly on the pairwise test, and show no first-item, missing-item, or symbolic-distance effects, suggesting that although pigeons can learn to respond to five items in a specific order, they do not form a representation of the sequential order of those items. We discuss the extent to which the difference in performance between birds and primates on the serial-order task reflects a difference in cognitive abilities, or whether the difference can be attributed to noncognitive factors.

We review our studies examining neural correlates of directed forgetting and executive control in the avian prefrontal cortex. One of the fundamental forms of executive control is the ability to selectively filter information, retaining that which is critical for the current purposes and discarding that which is not. In our first experiment, we trained birds on a directed-forgetting version of a delayed matching-to-sample task. Following a sample stimulus, a bird heard either a remember tone indicating that a memory test would follow, or a forget tone indicating that no memory test would be given. We found that neural activity in the avian prefrontal cortex increased when the bird was told to remember, and decreased when the bird was told to forget. Behavioral probe tests confirmed that the animals were forgetting on forget trials. Although the sustained activation observed on remember trials and the absence of such activation on forget trials could be a code of remembering and forgetting the sample stimulus, it could also be a code of the possibility of obtaining a reward. To address this issue we conducted a second study in which we used three cues: remember, forget, and forget-reward. The forget-reward cue instructed the subject to forget the sample yet at the same time provided a free reward. Neural activity on forget-reward trials matched that on remember trials tentatively indicating that the sustained activation on remember trials might be a reward code rather than a sample stimulus code. Behavioral probe tests, however, failed to indicate that the animals were forgetting on forget-reward trials, and hence it still is possible that the sustained activation could be a code for memory of the sample stimulus.

Bartolomeo Panizza was the first person to produce experimental and clinical evidence for a visual area in the posterior cerebral cortex. We here provide the first translation of this work entitled “Observations on the optic nerve” originally published in Italian in 1855. We also review the state of knowledge of the brain around Panizza’s time, summarize his career, and consider why his work was ignored.