Associative representations in lateral intraparietal (LIP) area
The primate brain is adept at rapidly making and breaking associations. Increasing evidence suggests that parietal cortex plays a role in encoding learned associations between visual stimuli. Here we tested the hypothesis that the lateral intraparietal area (LIP) can reflect learned stimulus-stimulus associations between multiple types of visual stimuli.
We trained two monkeys to group six shapes into three pairs and to perform a delayed pair association (DPA) task in which they viewed a sample shape (650 ms), delay (1500 ms), and test shape (650 ms). During the test period, the monkeys had to release a lever if the test shape was the pair-associate of the sample shape for a juice reward. We recorded from 112 LIP neurons in two animals during the DPA task and found that a majority was shape selective (Kruskal-Wallis test, p < 0.01). Moreover, many neurons (permutation test, p < 0.05) had activity that robustly reflected the learned associations: the spike rate evoked by a particular shape was most similar to that evoked by its pair-associate.
Our lab previously showed that LIP neurons can reflect the learned significance of visual motion during a direction-categorization task (Freedman and Assad, 2006). To test whether the same population of LIP neurons reflects associations between both motion and shape stimuli, we recorded from 45 neurons as a monkey switched between tasks. We computed an index to quantify the influence of learned associations on neuronal activity. In both tasks, the index revealed a significant tendency for neurons to respond similarly to stimuli from the same category or pair (t-test, p <; 0.01 for each task). Furthermore, many cells reflected both the shape pairs and motion categories (permutation test, p < 0.05), and indices for the two groupings were positively correlated (r = 0.46, p < 0.01).
These results suggest that LIP neurons can convey non-spatial signals about the learned associations of visual stimuli within their receptive fields (RFs). LIP cells are also selective for the location of visual stimuli or saccadic targets. We tested whether the same neurons encode spatial and non-spatial information by having a monkey switch between a memory delayed saccade task, to reveal spatial signals, and shape DPA task with stimuli confined to RFs, to reveal non-spatial signals. Many cells were robustly modulated by both tasks (permutation and Kruskal-Wallis tests, p < 0.05), indicating that single LIP neurons can reflect both spatial and non-spatial signals. In addition to its role in spatial processing, our results suggest that LIP can also reflect non-spatial information about the learned significance of, or relationship between, visual stimuli.
Conference:
Computational and systems
neuroscience 2009, Salt Lake City, UT, United States, 26 Feb - 3 Mar, 2009.
Presentation Type:
Poster Presentation
Topic:
Poster Presentations
Citation:
(2009). Associative representations in lateral intraparietal (LIP) area.
Front. Syst. Neurosci.
Conference Abstract:
Computational and systems
neuroscience 2009.
doi: 10.3389/conf.neuro.06.2009.03.145
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Received:
02 Feb 2009;
Published Online:
02 Feb 2009.