Biconditional Discrimination Tasks Research Articles

Context coding in the mouse nucleus accumbens modulates motivationally relevant information

Neural activity in the nucleus accumbens (NAc) is thought to track fundamentally value-centric quantities linked to reward and effort. However, the NAc also contributes to flexible behavior in ways that are difficult to explain based on value signals alone, raising the question of if and how nonvalue signals are encoded in NAc. We recorded NAc neural ensembles while head-fixed mice performed an odor-based biconditional discrimination task where an initial discrete cue modulated the behavioral significance of a subsequently presented reward-predictive cue. We extracted single-unit and population-level correlates related to the cues and found value-independent coding for the initial, context-setting cue. This context signal occupied a population-level coding space orthogonal to outcome-related representations and was predictive of subsequent behaviorally relevant responses to the reward-predictive cues. Together, these findings support a gating model for how the NAc contributes to behavioral flexibility and provide a novel population-level perspective from which to view NAc computations.

Elemental and non-elemental olfactory learning in Drosophila

Brain complexity varies across many orders of magnitude between animals, and it is often assumed that complexity underpins cognition. It is thus important to explore the cognitive capacity of widely used model organisms such as Drosophila. We systematically investigated the fly’s ability to learn discriminations involving compound olfactory stimuli associated with shock. Flies could distinguish binary mixtures (AB+ CD-), including overlapping mixtures (AB+ BC-). They could learn positive patterning (AB+A- B-) but could not learn negative patterning (A+ B+ AB-) or solve a biconditional discrimination task (AB+ CD+ AC- BD-). Learning about the elements of a compound (AB+) was not affected by prior conditioning of one of the elements (A+ AB+): flies do not exhibit blocking in this task. We compare these results with the predictions from simulation of several well-known theoretical models of learning, and find none are fully consistent with the overall pattern of observed behaviour.

Rat prefrontal dopamine and cognitive control: Impaired and enhanced conflict performance.

It has been proposed that the cognitive dysfunction observed in patients with schizophrenia reflects a failure in cognitive control, in particular an inability to use task-relevant information to guide behavior. Using a prefrontal-dependent task designed to reflect aspects of cue and response conflict seen in human cognitive paradigms, we examined the influence of prefrontal dopamine receptor manipulation on the contextual control of response conflict. Rats were trained on two biconditional discrimination tasks, one auditory and one visual, in two discriminably different contexts. At test, audiovisual compounds of these training stimuli were presented, in extinction, in each of the training contexts. These compounds were formed in such a way that the individual elements previously dictated different responses during training, termed incongruent trials. Studies have shown that rats use contextual information to disambiguate the conflicting information provided by incongruent compounds, responding in manner that is appropriate to the stimulus element that was trained in the test context. Direct infusion of the D1 receptor agonist SKF-38393 into the prelimbic cortex was found to modulate incongruent trial performance in a manner that was dependent upon baseline performance: animals in the low baseline group demonstrated improved incongruent performance following infusion of SKF-38393 into the prelimbic cortex. In contrast, high performers showed a reduction in accuracy during incongruent compounds. This paradigm provides a reliable framework for assessing the efficacy of preclinical agents in treating the cognitive impairments seen in frontal-related disorders such as schizophrenia.

Excitatory, Inhibitory, and Structural Plasticity Produce Correlated Connectivity in Random Networks Trained to Solve Paired-Stimulus Tasks

The pattern of connections among cortical excitatory cells with overlapping arbors is non-random. In particular, correlations among connections produce clustering – cells in cliques connect to each other with high probability, but with lower probability to cells in other spatially intertwined cliques. In this study, we model initially randomly connected sparse recurrent networks of spiking neurons with random, overlapping inputs, to investigate what functional and structural synaptic plasticity mechanisms sculpt network connections into the patterns measured in vitro. Our Hebbian implementation of structural plasticity causes a removal of connections between uncorrelated excitatory cells, followed by their random replacement. To model a biconditional discrimination task, we stimulate the network via pairs (A + B, C + D, A + D, and C + B) of four inputs (A, B, C, and D). We find networks that produce neurons most responsive to specific paired inputs – a building block of computation and essential role for cortex – contain the excessive clustering of excitatory synaptic connections observed in cortical slices. The same networks produce the best performance in a behavioral readout of the networks’ ability to complete the task. A plasticity mechanism operating on inhibitory connections, long-term potentiation of inhibition, when combined with structural plasticity, indirectly enhances clustering of excitatory cells via excitatory connections. A rate-dependent (triplet) form of spike-timing-dependent plasticity (STDP) between excitatory cells is less effective and basic STDP is detrimental. Clustering also arises in networks stimulated with single stimuli and in networks undergoing raised levels of spontaneous activity when structural plasticity is combined with functional plasticity. In conclusion, spatially intertwined clusters or cliques of connected excitatory cells can arise via a Hebbian form of structural plasticity operating in initially randomly connected networks.

Contextual control of biconditional task performance: Evidence for cue and response competition in rats

A novel paradigm is presented that was designed to mimic aspects of cue and response competition seen in humans in conflict procedures such as the Stroop task. Rats were trained simultaneously on two biconditional discrimination tasks, one auditory and one visual, in two different contexts: C1, in which A1:LP1-->R, A2:LP2-->R; and C2, in which V1:LP1-->R, V2:LP2-->R, where C1/C2 represent different training contexts (produced by different operant chambers), A1/A2 are different auditory cues, V1/V2 are different visual cues, LP1/LP2 are discrete operant responses, and R is reward. At test, rats received presentations of audiovisual compounds of these training stimuli in extinction. These compounds had dictated either the same (A1V1 or A2V2) or different (A1V2 or A2V1) responses during training: termed congruent and incongruent trials, respectively. Experiment 1 showed that following equal training on the two biconditional tasks, the contextual cues came to control responding to conflicting information provided by incongruent stimulus compounds such that animals responded according to the stimulus element previously trained in that test context. Experiment 2 demonstrated that differential training on the biconditional discriminations (with rats receiving training on the two discriminations in the ratio 3:1) resulted in greater interference from the overtrained task when animals were tested in the undertrained context. This finding is similar to the classic Stroop asymmetry seen in human performance whereby dominant word reading interferes with colour naming for incongruent colour-word compounds. Further analysis also revealed some evidence for a reverse Stroop effect in which the undertrained stimulus element interfered with performance on the overtrained task.

No evidence for visual context-dependency of olfactory learning in Drosophila

How is behaviour organised across sensory modalities? Specifically, we ask concerning the fruit fly Drosophila melanogaster how visual context affects olfactory learning and recall and whether information about visual context is getting integrated into olfactory memory. We find that changing visual context between training and test does not deteriorate olfactory memory scores, suggesting that these olfactory memories can drive behaviour despite a mismatch of visual context between training and test. Rather, both the establishment and the recall of olfactory memory are generally facilitated by light. In a follow-up experiment, we find no evidence for learning about combinations of odours and visual context as predictors for reinforcement even after explicit training in a so-called biconditional discrimination task. Thus, a ‘true’ interaction between visual and olfactory modalities is not evident; instead, light seems to influence olfactory learning and recall unspecifically, for example by altering motor activity, alertness or olfactory acuity.

Both motivational and training factors affect response conflict choice performance in rats

Rats were trained on two biconditional discrimination tasks, in two different contexts, and were rewarded with two different outcomes. At test, they received presentations of audiovisual compounds of these training stimuli, in extinction. These compounds were formed in such way that the individual elements had dictated either the same (congruent trials) or different (incongruent trials) responses during training, and each stimulus element had previously been rewarded with a different outcome. Previous research has shown that rats use the contextual cues to disambiguate the conflicting response information provided by incongruent stimulus compounds. Experiment 1 demonstrated that this contextual control was goal-directed in the sense that it depended on the current value of the outcome and Experiment 2 demonstrated that both the training history of the biconditional stimuli and motivational influences influenced the contextual control of responding on incongruent trials. These results are discussed in relation to current models of choice behaviour.

Olfactory learning and behaviour are ‘insulated’ against visual processing in larval Drosophila

We investigate the organization of behaviour across sensory modalities, using larval Drosophila melanogaster. We ask whether olfactory learning and behaviour are affected by visual processing. We find that: (1) Visual choice does not affect concomitant odour choice. (2) Visual context does not influence odour learning, nor do changes of visual context between training and test affect retrieval of odour memory. (3) Larvae cannot solve a biconditional discrimination task, despite generally permissive conditions. In this task, larvae are required to establish conditional associations: in light, one odour is rewarded and the other one is not, whereas in dark the opposite contingency is established. After such training, choice between the two odours is equal under light and dark testing conditions, suggesting that larvae do not establish odour memories specifically for one visual context only. Together, these data suggest that, in larval Drosophila, olfactory learning and behaviour are 'insulated' against visual processing.

An olfactory biconditional discrimination in the mouse

Male CD-1 mice were given a biconditional discrimination task with four odors; A, B, C, and D. Mice were presented with odor compounds AC+, BD+, BC−, AD− for thirteen days. Pieces of odorized filter paper were placed in the bottom of odor pots and covered with bedding. On reinforced AC and BD trials, sugar was buried in the bedding, and on nonreinforced AD and BC trials no sugar was present. Following training, simultaneous nonreinforced tests were given between AD and AC, and between BC and BD. The mice spent more time digging in the previously reinforced odor compounds than in the previously nonreinforced compounds. In a second experiment, mice were conditioned to dig in AC+ and not BD−. In a subsequent test with the separate elements they dug more in A and C than in B and D, indicating that the biconditional discrimination had not been solved on the basis of complete perceptual blending. The data demonstrate that mice are capable of olfactory configural learning when solving a biconditional discrimination.

MEDIAL PREFRONTAL CORTEX LESIONS ABOLISH CONTEXTUAL CONTROL OF COMPETING RESPONSES

There is much debate as to the extent and nature of functional specialization within the different subregions of the prefrontal cortex. The current study was undertaken to investigate the effect of damage to medial prefrontal cortex subregions in the rat. Rats were trained on two biconditional discrimination tasks, one auditory and one visual, in two different contexts. At test, they received presentations of audiovisual compounds of these training stimuli in extinction. These compounds had dictated either the same (congruent trials) or different (incongruent trials) responses during training. In sham-operated controls, contextual cues came to control responding to conflicting information provided by incongruent stimulus compounds. Experiment 1 demonstrated that this contextual control of responding was not evident in individual rats with large amounts of damage that included the prelimbic and cingulate subregions of the prefrontal cortex. Experiment 2 further dissociated the result of Experiment 1, demonstrating that lesions specific to the anterior cingulate cortex were sufficient to produce a deficit early on during presentation of an incongruent stimulus compound but that performance was unimpaired as presentation progressed. This early deficit suggests a role for the anterior cingulate cortex in the detection of response conflict, and for the medial prefrontal cortex in the contextual control of competing responses, providing evidence for functional specialization within the rat prefrontal cortex.

Insights into the nature of fronto-temporal interactions from a biconditional discrimination task in the monkey

Previous work in monkeys has shown that both frontal and inferior temporal cortices are required to solve visual learning tasks. When communication between these cortical areas is prevented within the same hemisphere by crossed lesions of the frontal cortex in one hemisphere and the inferior temporal cortex in the opposite hemisphere, most learning tasks are impaired, but learning of object-reward associations is unimpaired. The current experiment aims to understand further the role of the interaction between the frontal and inferior temporal cortices in learning tasks. We trained monkeys on a biconditional discrimination task, in which different visual cues guided behaviour towards choice objects. One visual cue predicted immediate delivery of reward to a correct response, the other visual cue predicted a delayed delivery of reward to a correct response. Pre-operative behavioural data clearly shows that the monkeys form expectations of the reward outcome for the individual cues and choice objects. Crossed lesions of frontal and inferior temporal cortices, however, produce no impairment on this task. The result suggests (in combination with previous experiments) that task difficulty does not determine the reliance of a task on interactions between the frontal cortex and the inferior temporal cortex within the same hemisphere. Instead, we propose that tasks that can be solved by using expectation of the reward outcome do not require interaction of frontal and inferior temporal cortices within the same hemisphere. The results are discussed in the context of other data on frontal interactions with inferior temporal cortex in learning tasks.