Sustained activation and executive control in the avian prefrontal cortex

Abstract

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. © 2008 Elsevier Inc. All rights reserved.Keywords: Sustained activation; Neural correlates of memory; Delay cells; Executive control; Prefrontal cortex; Nidopallium caudolaterale That we remember is self evident, yet how remembering is expressed in the activity of neurons is almost completely unknown. One possible mechanism that has been proposed is that of sustained activation [4,9,20]. Sustained activation is best understood with reference to the delayed matching-to-sample (DMS) task, a classic test of short-term memory in animals [23]. At the end of an intertrial interval (ITI), a sample stimulus (e.g., a circle or a line) is presented on the center of three projectors (see Fig. 1). After the subject makes a response to the sample stimulus, the sample stimulus is turned off for a period of time (delay) during which memory for the sample stimulus is activated. At the end of the delay period, both stimuli (circle and line) appear on the side projectors (comparison). A correct response requires * Corresponding author.E-mail address: colombo@psy.otago.ac.nz (M. Colombo). the subject to select the comparison stimulus that was the same as the sample stimulus. In the case of trial n in Fig. 1, the correct response is to press the circle stimulus, which results in a reward. Selecting the incorrect sti...

Delayed matching-to-sample: A tool to assess memory and other cognitive processes in pigeons

“…on a remember-cued trial (Kendrick et al, 1981; but see Grant and Barnet, 1991). Consistent with this interpretation of the different effects of forget cue trials depending on the events that followed the forget cue in training, Milmine et al (2008) found that neurons in the nidopallium caudolaterale (a proposed pigeon analog to the mammalian prefrontal cortex) differentially fired on remember and forget cues relative to the intertrial interval. However, in a second experiment they found when forget cue trials ended in reinforcement, the neurons showed the same neuronal activity levels as on remember cue trials.…”

Cross-Modal Associative Mnemonic Signals in Crow Endbrain Neurons

“…In the same vein, Rose and Colombo [4] found 67% of neurons with sustained delay activity, the majority of which responded only for a to-be-remembered stimulus, but not after the pigeon was instructed to forget the stimulus. Several follow-up studies demonstrated that this activity was based mainly on reward prediction [29][30][31]. Similarly, if different auditory stimuli are associated with one of two response keys, it is difficult to dissociate responses representing the associations or rather preparatory left versus right motor activity [32].…”

Hippocampal memory consolidation during sleep: a comparison of mammals and birds

“…Divac and coworkers were the first to propose that the avian equivalent of the PFC is the NCL (Mogensen & Divac, 1982, 1993; Divac, Mogensen & Björklund, 1985). Since then a growing body of research has accumulated supporting the notion that the NCL and PFC are analogous structures involved in performing high‐order cognitive processes (Reiner, 1986; Güntürkün, 1997; Hartmann & Güntürkün, 1998; Braun et al , 1999; Kalt, Diekamp & Güntürkün, 1999; Diekamp, Kalt & Güntürkün, 2002; Rose & Colombo, 2005; Milmine, Rose & Colombo, 2008; reviewed in Güntürkün, 2005 a , b ; Kirsch, Güntürkün & Rose, 2008; Rose, Güntürkün & Kirsch, 2009). Although the PFC and NCL both develop from the pallium (dorsal portion of the neural tube), they originate from different pallial sectors, and therefore reflect analogous structures (see ).…”