Activity of neurons in anterior inferior temporal cortex during a short-term memory task.

@article{citeulike:444871, abstract = {Inferior temporal (IT) cortex of primates is known to play an important role in visual memory. Previous studies of IT neurons during performance of working memory tasks have found modulation of responses when a current stimulus matched an item in memory; however, this effect was lost if other stimuli intervened in the retention interval. To examine how IT cortex retains memories while new stimuli are activating the cells, we recorded from IT neurons while monkeys performed a delayed matching-to-sample task, with multiple intervening items between the sample and matching test stimulus. About half of the cells responded differently to a test stimulus if it matched the sample, and this difference was maintained following intervening stimuli. For most of the affected cells, the responses to matching stimuli were suppressed; however, for a few cells the opposite effect was seen. Temporal contiguity alone could not explain the results, as there was no modulation of responses when a stimulus on one trial was repeated on the next trial. Thus, an active reset mechanism appears to restrict the memory comparison to just the stimuli presented within a trial. The suppressive effects appear to be generated within or before IT cortex since the suppression of response to matching stimuli began almost immediately with the onset of the visual response. The memory of the sample stimulus affected not only the responses to matching stimuli but also those to nonmatching stimuli. There was suggestive evidence that the more similar a nonmatching stimulus to the sample, the more the response was suppressed. About a quarter of the cells showed stimulus-selective activity in the delay interval following the sample. However, this activity appeared to be eliminated by intervening stimuli. Thus, it is unlikely that delay-interval activity in IT contributed to the performance of this particular version of delayed matching to sample. To determine how much information about the match-nonmatch status of the stimulus was conveyed by individual neurons, we analyzed the responses with discriminant analysis. The responses of an individual IT neuron could be used to classify a stimulus as matching or nonmatching on about 60\% of the trials. To achieve the same performance as the animal would require averaging the responses of a minimum of 25 IT neurons. There was no evidence that mnemonic information was carried by temporal variations in the spike trains. By contrast, there was a modest amount of temporal variation in sensory responses to different visual stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)}, address = {Laboratory of Neuropsychology, National Institute of Mental Health, Bethesda, Maryland 20892.}, author = {Miller, E. K. and Li, L. and Desimone, R. }, citeulike-article-id = {444871}, comment = {Inferior temporal cortex (IT) is thought to be related to visual memory in many studies. Most of the studies were done with delayed matching-to-sample task, where the animal had to retain the memory of a sample during the "delay." The performance was often affected or tenuated if the animal was distracted by other stimuli. While most experiments focus on the "blank" memory retention, the current study looks to see how the cells react to intervening stimuli during the delay. The task starts with a sample, and the trained animal has to grasp a bar. Following the sample is 0-5 test items. When the item matches the sample, the animal has to release the bar. If the response is correct, the animal will get orange juice as reward. When the stimulus matches with the sample stimulus, the response is suppresed. Also, the responses to non-matching stimuli were also affected by the stimulus that's held in memory. A weak link shows that the more similar a stimulus is to the sample, the more the response is to be suppresed. However, the suppression doesn't carry accross trials. Thus it is suggested that "an active process either clears out or resets the memory traces of stimuli from one trial to the next" (p.1475). The author propose two populations of IT cells that contribute to memory: one is "sensory cells" that providea referent, and the "adaptive mnemonic filter cells". The difference in response between these two groups of cells is the measure of similarity between the stimulus and sample stimulus. }, issn = {0270-6474}, journal = {J Neurosci}, keywords = {cortex, inferior, memory, temporal, visual}, month = {April}, number = {4}, pages = {1460--1478}, posted-at = {2006-03-14 08:26:40}, priority = {0}, title = {Activity of neurons in anterior inferior temporal cortex during a short-term memory task.}, url = {http://www.jneurosci.org/cgi/content/abstract/13/4/1460}, volume = {13}, year = {1993} }

TY - JOUR ID - citeulike:444871 L3 - citeulike-article-id:444871 TI - Activity of neurons in anterior inferior temporal cortex during a short-term memory task. JF - J Neurosci VL - 13 IS - 4 SP - 1460 EP - 1478 AD - Laboratory of Neuropsychology, National Institute of Mental Health, Bethesda, Maryland 20892. SN - 0270-6474 N2 - Inferior temporal (IT) cortex of primates is known to play an important role in visual memory. Previous studies of IT neurons during performance of working memory tasks have found modulation of responses when a current stimulus matched an item in memory; however, this effect was lost if other stimuli intervened in the retention interval. To examine how IT cortex retains memories while new stimuli are activating the cells, we recorded from IT neurons while monkeys performed a delayed matching-to-sample task, with multiple intervening items between the sample and matching test stimulus. About half of the cells responded differently to a test stimulus if it matched the sample, and this difference was maintained following intervening stimuli. For most of the affected cells, the responses to matching stimuli were suppressed; however, for a few cells the opposite effect was seen. Temporal contiguity alone could not explain the results, as there was no modulation of responses when a stimulus on one trial was repeated on the next trial. Thus, an active reset mechanism appears to restrict the memory comparison to just the stimuli presented within a trial. The suppressive effects appear to be generated within or before IT cortex since the suppression of response to matching stimuli began almost immediately with the onset of the visual response. The memory of the sample stimulus affected not only the responses to matching stimuli but also those to nonmatching stimuli. There was suggestive evidence that the more similar a nonmatching stimulus to the sample, the more the response was suppressed. About a quarter of the cells showed stimulus-selective activity in the delay interval following the sample. However, this activity appeared to be eliminated by intervening stimuli. Thus, it is unlikely that delay-interval activity in IT contributed to the performance of this particular version of delayed matching to sample. To determine how much information about the match-nonmatch status of the stimulus was conveyed by individual neurons, we analyzed the responses with discriminant analysis. The responses of an individual IT neuron could be used to classify a stimulus as matching or nonmatching on about 60% of the trials. To achieve the same performance as the animal would require averaging the responses of a minimum of 25 IT neurons. There was no evidence that mnemonic information was carried by temporal variations in the spike trains. By contrast, there was a modest amount of temporal variation in sensory responses to different visual stimuli.(ABSTRACT TRUNCATED AT 400 WORDS) KW - cortex KW - inferior KW - memory KW - temporal KW - visual N1 - Inferior temporal cortex (IT) is thought to be related to visual memory in many studies. Most of the studies were done with delayed matching-to-sample task, where the animal had to retain the memory of a sample during the "delay." The performance was often affected or tenuated if the animal was distracted by other stimuli. While most experiments focus on the "blank" memory retention, the current study looks to see how the cells react to intervening stimuli during the delay. The task starts with a sample, and the trained animal has to grasp a bar. Following the sample is 0-5 test items. When the item matches the sample, the animal has to release the bar. If the response is correct, the animal will get orange juice as reward. When the stimulus matches with the sample stimulus, the response is suppresed. Also, the responses to non-matching stimuli were also affected by the stimulus that's held in memory. A weak link shows that the more similar a stimulus is to the sample, the more the response is to be suppresed. However, the suppression doesn't carry accross trials. Thus it is suggested that "an active process either clears out or resets the memory traces of stimuli from one trial to the next" (p.1475). The author propose two populations of IT cells that contribute to memory: one is "sensory cells" that providea referent, and the "adaptive mnemonic filter cells". The difference in response between these two groups of cells is the measure of similarity between the stimulus and sample stimulus. AU - Miller, EK AU - Li, L AU - Desimone, R PY - 1993/04// UR - http://www.jneurosci.org/cgi/content/abstract/13/4/1460 ER -