Task phase‐specific involvement of the rat posterior parietal cortex in performance of the TUNL task

Abstract

The posterior parietal cortex (PPC) participates in cognitive processes including working memory (WM), sensory evidence accumulation, and perceptually guided decision making. However, surprisingly little work has used temporally precise manipulations to dissect its role in different epochs of behavior taking place over short timespans, such as WM tasks. As a result, a consistent view of the temporally precise role of the PPC in these processes has not been described. In the present study, we investigated the temporally specific role of the PPC in the Trial‐Unique, Nonmatching‐to‐Location (TUNL) task, a touchscreen‐based, visuospatial WM task that relies on the PPC. To disrupt PPC activity in a temporally precise manner, we applied mild intracranial electrical stimulation (ICES). We found that intra‐PPC ICES (100 μA) significantly impaired accuracy in TUNL without significantly altering response latency. Moreover, we found that the impairment was specific to ICES applied during the delay and test phases of TUNL. Consistent with previous reports showing delay‐ and choice‐specific neuronal activity in the PPC, the results provide evidence that the rat PPC is required for maintaining memory representations of stimuli over a delay period as well as for making successful comparisons and choices between test stimuli. In contrast, the PPC appears not to be critical for initial encoding of sample stimuli. This pattern of results may indicate that early encoding of visual stimuli is independent of the PPC or that the PPC becomes engaged only when visual stimuli are spatially complex or involve memory or decision making.

The Touchscreen‐Based Trial‐Unique, Nonmatching‐To‐Location (TUNL) Task as a Measure of Working Memory and Pattern Separation in Rats and Mice

“…A 5‐s timeout period is universally applied. Throughout Punish Incorrect, Initial TUNL, and Full TUNL Training, a performance accuracy criterion of around 70%‐80% of stable performance is promoted (Anderson et al., 2020; Davies et al., 2017; Horner et al., 2013; Hurtubise et al., 2017; Lee et al., 2020; Oomen et al., 2013; Scott et al., 2019, 2021). There has, however, been the rare occasion where the required performance was set at a stable performance accuracy of above 50% (McAllister et al., 2013).…”

“…Following the acquisition of all the contributing rules, and with sufficient opportunity to practice the combinations of the rules in the Full TUNL task, specific probing sessions can now be implemented. During the Full TUNL task, the delay period is increased to around a 6‐s delay, with slight fluctuation by a second or two between researchers (Anderson et al., 2020; Davies et al., 2017; Horner et al., 2013; Hurtubise et al., 2017; Lee et al., 2020; Oomen et al., 2013; Scott et al., 2019, 2021). The delay period and resulting cognitive load can be dictated by the intended pharmacological intervention and evaluated parameters.…”

“…In the Basic Protocols, the criteria for each session are based on the observed efficacy of multiple successful applications of the TUNL task with these set criteria (Anderson et al., 2020; Davies, Hurtubise, Greba, & Howland, 2017; Scott et al., 2021; Scott, Roebuck, Greba, & Howland, 2019). Other studies within the literature use similar progressions between sessions for the TUNL task, but have different required criteria at each stage.…”

“…Extending sessions gives rats increased opportunities to learn the desired rules. Not only does this reduce training time to reach criterion and ultimately complete training, but it helps defend against confounding “mediating strategies” used by rats (Anderson et al., 2020; Davies et al., 2017; Scott et al., 2019; Scott et al., 2021). This approach is implemented throughout Must Touch, Must Initiate, and Punish Incorrect Training (Basic Protocols 3‐4).…”

Touchscreen response technology and the power of stimulus‐based approaches in freely behaving animals

“…Though perseverative errors were greater in XY than XX mice, SCC did not impact regressive errors or the number of trials required to reach criterion, suggesting that learning strategy but not overall learning rate is affected by SCC. Another example of subprocess sensitivity is Scott and colleagues' 10 trial unique nonmatch to location (TUNL) task, a test of spatial working memory in rats. Scott et al found that intraposterior parietal cortex intracranial electrical stimulation impaired TUNL accuracy, without affecting response latencies to the sample, providing evidence that rat posterior parietal cortex is required in maintaining a representation of stimuli over a delay period, but not in the encoding of sample stimuli.…”