The brain dynamically changes its input-output relationship depending on the behavioral state and context in order to optimize information processing. At the molecular level, cholinergic/monoaminergic transmitters have been extensively studied as key players for the state/context-dependent modulation of brain function. In this paper, we review how cortical visual information processing in the primary visual cortex (V1) of macaque monkey, which has a highly differentiated laminar structure, is optimized by serotonergic and cholinergic systems by examining anatomical and in vivo electrophysiological aspects to highlight their similarities and distinctions. We show that these two systems have a similar layer bias for axonal fiber innervation and receptor distribution. The common target sites are the geniculorecipient layers and geniculocortical fibers, where the appropriate gain control is established through a geniculocortical signal transformation. Both systems exert activity-dependent response gain control across layers, but in a manner consistent with the receptor subtype. The serotonergic receptors 5-HT1B and 5HT2A modulate the contrast-response curve in a manner consistent with bi-directional response gain control, where the sign (facilitation/suppression) is switched according to the firing rate and is complementary to the other. On the other hand, cholinergic nicotinic/muscarinic receptors exert mono-directional response gain control without a sign reversal. Nicotinic receptors increase the response magnitude in a multiplicative manner, while muscarinic receptors exert both suppressive and facilitative effects. We discuss the implications of the two neuromodulator systems in hierarchical visual signal processing in V1 on the basis of the developed laminar structure.
Noradrenaline (NA) is released from the locus coeruleus in the brainstem to almost the whole brain depending on the physiological state or behavioral context. NA modulates various brain functions including vision, but many questions about the functional role of its effects and mechanisms remain unclear. To explore these matters, we focused on three questions, 1) whether NA improves detectability of a behavior-relevant visual stimulus, 2) which receptor subtypes contribute to the NA effects, and 3) whether the NA effects are specific for visual features such as spatial frequency (SF). We measured contrast sensitivity in rats by a two-alternative forced choice visual detection task and tested the effects of NA receptor blockers in three SF conditions. Propranolol, a β-adrenergic receptor inhibitor, significantly decreased contrast sensitivity, but neither prazosin nor idazoxan, α1- and α2-adrenergic receptor inhibitors, respectively, had an effect. This β blocker effect was observed only at optimal SF. These results indicate that endogenous NA enhances visual detectability depending on stimulus spatial properties via mainly β-adrenergic receptors.
15Previous studies have shown that domestic chicks, Gallus gallus domesticus, trained in 16 a competitive foraging condition would subsequently develop a high degree of 17 impulsiveness in an intertemporal choice paradigm. Competition inevitably causes 18 variance in the amount of food that the foragers gain. However, it is not known whether 19 the food variance is causally linked with the impulsiveness. In experiment 1, we 20 compared four groups of chicks trained in combinations of two social conditions 21 (pseudocompetition or isolated) and two food conditions (variable or constant food). 22The food variance was introduced by varying the number of grains in each trial 23 according to a binomial distribution. The subject chick was separated from the 24 コメント [AT1]: Author: 'variant' means 'different'. I think you mean 'variable'.2 competitors by a transparent wall, and no actual interference occurred. Chicks were 25 subsequently tested in binary choices between a small reward after a short delay (SS) 26 and a large reward after a long delay (LL) in an isolated and constant food condition. If 27 chicks had been trained under the pseudocompetition and variable food, they chose LL 28 significantly less frequently than the other three groups. The effect disappeared when 29 the LL delay was omitted, suggesting that chicks accurately memorized the food amount. 30The food variance is thus a necessary condition for the stronger temporal discounting. 31Otherwise, the observed effect could be ascribed to a paradoxical risk proneness 32 associated with the variable option. In experiment 2, we compared four groups of chicks 33 in which food amount varied either in SS or LL, or both. The subsequent binary choice 34 tests revealed that the chicks chose SS irrespective of whether SS or LL had varied. 35These results cannot be explained in terms of a greater risk-prone choice of the variable 36 option. Coincidence of perceived competition and food variance, at least in one option, 37 is sufficient for chicks to develop choice impulsiveness. 38 39
Serotonin (5-HT) is a neuromodulator secreted from serotonergic neurons located in the pons and upper brain stem in a behavioral context-dependent manner. The serotonergic axon terminals innervate almost the whole brain, causing modulatory actions on various brain functions including vision. Our previous study demonstrated the visual responses of neurons in the primary visual cortex (V1) of anesthetized monkeys were modulated by the activation of 5-HT receptors depending on the response magnitude, in which 5-HT2A receptor-selective agonists enhanced weak visual responses but not strong responses. This observation suggests that the activation of serotonergic receptors modulates neuronal visual information processing to improve the behavioral detectability of a stimulus. However, it remains unknown if 5-HT improves visual detectability at the behavioral level. To investigate this point, visual detectability was measured as contrast sensitivity (CS) in freely moving rats using a two-alternative forced-choice visual detection task (2AFC-VDT) combined with the staircase method. The grating contrast was decreased or increased step by step after a correct choice (hit) or incorrect choice (miss), respectively. CS was evaluated as an inverse value of the visual contrast threshold. The effect of the intraperitoneal administration of fluoxetine (FLX, 5 mg/kg), a selective serotonin reuptake inhibitor, on CS was tested. The CS of rats was significantly higher in FLX than control conditions, and the drug effect showed specificity for the spatial frequency (SF) of a grating stimulus, in which CS improvement was observed at optimal SF but not non-optimal high SF. Thus, we conclude that endogenously-secreted serotonin in the brain improves visual detectability, which may be mediated by vision-related neurons acquiring SF information of the visual stimulus. PLOS ONEPLOS ONE | https://doi.org/10.
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