The prefrontal cortex (PFC) is known to be critically involved in strategy switching, attentional set shifting, and inhibition of prepotent responses. A central feature of this kind of behavioral flexibility is the ability to resolve conflicting response tendencies, suggesting a general role of the PFC in resolving interference. If so, the PFC should also be involved in memory retrieval, which involves competition between potential retrieval targets. Moreover, the PFC should be needed whenever interference is high, regardless of the strategic or attentional requirements of the task. To test this hypothesis, we temporarily inactivated the mPFC with muscimol and tested rats on several olfactory learning tasks. Rats given muscimol were able to learn a few discrimination problems when they were learned one at a time. However, they were severely impaired when they had to learn and remember many odors concurrently. Rats given muscimol also suffered greater interference when learning two lists of conflicting odor discrimination problems. Additionally, temporary mPFC inactivation during the acquisition of one set of odor memories actually improved the ability to learn a new set of conflicting odor memories. This paradoxical release from interference suggests that the mPFC plays an important role in acquiring and promoting the long term retrieval of memories. These results suggest that the mPFC plays a general role in resolving interference and that this is a key aspect of behavioral flexibility.
Trajectory-dependent coding in dorsal CA1 of hippocampus has been evident in various spatial memory tasks aiming to model episodic memory. Hippocampal neurons are considered to be trajectory-dependent if the neuron has a place field located on an overlapping segment of two trajectories and exhibits a reliable difference in firing rate between the two trajectories. It is unclear whether trajectory-dependent coding in hippocampus is a mechanism used by the rat to solve spatial memory tasks. A first step in answering this question is to compare results between studies using tasks that require spatial working memory and those that do not. We recorded single units from dorsal CA1 of hippocampus during performance of a discrete-trial, tactile-visual conditional discrimination (CD) task in a T-maze. In this task, removable floor inserts that differ in texture and appearance cue the rat to visit either the left or right goal arm to receive a food reward. Our goal was to assess whether trajectory coding would be evident in the CD task. Our results show that trajectory coding was rare in the CD task, with only 12 of 71 cells with place fields on the maze stem showing a significant firing rate difference between left and right trials. For comparison, we recorded from dorsal CA1 during the acquisition and performance of a continuous spatial alternation task identical to that used in previous studies and found a proportion of trajectory coding neurons similar to what has been previously reported. Our data suggest that trajectory coding is not a universal mechanism used by the hippocampus to disambiguate similar trajectories, and instead may be more likely to appear in tasks that require the animal to retrieve information about a past trajectory, particularly in tasks that are continuous rather than discrete in nature.
The prefrontal cortex (PFC) plays a key role in behavioral flexibility, and the ability to resolve conflict from shifting strategies, task rules or attentional demands seems to be a hallmark of PFC function. Conflict also occurs in the domain of memory and the PFC plays an important role in the ability to cope with interference between competing retrieval targets. Previous studies often involved both interference and changes in task demands, which makes it difficult to determine the degree to which mnemonic interference per se engages PFC processing. We trained rats on a continuous matching to sample task in two conditions that varied in terms of the amount of interference present but not the task demands and found that temporary inactivation of the medial PFC caused a greater impairment in the high-interference condition. This result suggests that the PFC plays an important role in resolving interference which can be distinguished from its role in shifting task demands.
Harvesting and processing input combinations and product quality attributes for the Pacific whiting surimi industry were collected and analyzed. Multiple linear regression, neural networks, and M5-induction were used to determine significant variables in the industry. Significant factors included variables intrinsic to the fish (moisture content, salinity, pH, length, weight) and processing variables (processing time, storage temperature, harvest date, wash time, wash ratios). Most variables were highly interactive and nonlinear. Information derived from these models have implications for production and management decisions.
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