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Short-term memory trace in rapidly adapting synapses of inferior temporal cortex.

Sugase-Miyamoto Y, Liu Z, Wiener MC, Optican LM, Richmond BJ - PLoS Comput. Biol. (2008)

Bottom Line: We found that a large proportion (80%) of stimulus-selective neurons in area TE of macaque ITCs exhibit a memory effect during the stimulus interval.Neurons in perirhinal cortex did not show this correlation.Simulations of a matched filter model match the experimental results, suggesting that area TE neurons store a synaptic memory trace during short-term visual memory.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America.

ABSTRACT
Visual short-term memory tasks depend upon both the inferior temporal cortex (ITC) and the prefrontal cortex (PFC). Activity in some neurons persists after the first (sample) stimulus is shown. This delay-period activity has been proposed as an important mechanism for working memory. In ITC neurons, intervening (nonmatching) stimuli wipe out the delay-period activity; hence, the role of ITC in memory must depend upon a different mechanism. Here, we look for a possible mechanism by contrasting memory effects in two architectonically different parts of ITC: area TE and the perirhinal cortex. We found that a large proportion (80%) of stimulus-selective neurons in area TE of macaque ITCs exhibit a memory effect during the stimulus interval. During a sequential delayed matching-to-sample task (DMS), the noise in the neuronal response to the test image was correlated with the noise in the neuronal response to the sample image. Neurons in perirhinal cortex did not show this correlation. These results led us to hypothesize that area TE contributes to short-term memory by acting as a matched filter. When the sample image appears, each TE neuron captures a static copy of its inputs by rapidly adjusting its synaptic weights to match the strength of their individual inputs. Input signals from subsequent images are multiplied by those synaptic weights, thereby computing a measure of the correlation between the past and present inputs. The total activity in area TE is sufficient to quantify the similarity between the two images. This matched filter theory provides an explanation of what is remembered, where the trace is stored, and how comparison is done across time, all without requiring delay period activity. Simulations of a matched filter model match the experimental results, suggesting that area TE neurons store a synaptic memory trace during short-term visual memory.

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Predictions of response deviations by the deterministic model simulation.(A, B) Predictions of the deviations for TE (A) and perirhinal (B) neurons. Left column shows predictions of the deviations from the mean in the sample responses compared to the actual sample response deviations. Right column shows predictions for nonmatch response deviations. Variance explained is low in TE, but zero for perirhinal, which is a rough match to our data. (Format as in Figure 5.)
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pcbi-1000073-g006: Predictions of response deviations by the deterministic model simulation.(A, B) Predictions of the deviations for TE (A) and perirhinal (B) neurons. Left column shows predictions of the deviations from the mean in the sample responses compared to the actual sample response deviations. Right column shows predictions for nonmatch response deviations. Variance explained is low in TE, but zero for perirhinal, which is a rough match to our data. (Format as in Figure 5.)

Mentions: In Figure 6, instead of predicting the responses of the neurons to the sample or nonmatch stimulus on each trial, we predict the deviation of that response from its mean. This roughly matches what we found in the data (see Figure 3). The variance explained in the prediction of the response deviation was much less than the variance explained in the prediction of the response itself for perirhinal neurons (R2 = 0.05 and 0.06 for sample and nonmatch deviations in TE, and R2<0.001 for deviations in perirhinal neurons).


Short-term memory trace in rapidly adapting synapses of inferior temporal cortex.

Sugase-Miyamoto Y, Liu Z, Wiener MC, Optican LM, Richmond BJ - PLoS Comput. Biol. (2008)

Predictions of response deviations by the deterministic model simulation.(A, B) Predictions of the deviations for TE (A) and perirhinal (B) neurons. Left column shows predictions of the deviations from the mean in the sample responses compared to the actual sample response deviations. Right column shows predictions for nonmatch response deviations. Variance explained is low in TE, but zero for perirhinal, which is a rough match to our data. (Format as in Figure 5.)
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2366068&req=5

pcbi-1000073-g006: Predictions of response deviations by the deterministic model simulation.(A, B) Predictions of the deviations for TE (A) and perirhinal (B) neurons. Left column shows predictions of the deviations from the mean in the sample responses compared to the actual sample response deviations. Right column shows predictions for nonmatch response deviations. Variance explained is low in TE, but zero for perirhinal, which is a rough match to our data. (Format as in Figure 5.)
Mentions: In Figure 6, instead of predicting the responses of the neurons to the sample or nonmatch stimulus on each trial, we predict the deviation of that response from its mean. This roughly matches what we found in the data (see Figure 3). The variance explained in the prediction of the response deviation was much less than the variance explained in the prediction of the response itself for perirhinal neurons (R2 = 0.05 and 0.06 for sample and nonmatch deviations in TE, and R2<0.001 for deviations in perirhinal neurons).

Bottom Line: We found that a large proportion (80%) of stimulus-selective neurons in area TE of macaque ITCs exhibit a memory effect during the stimulus interval.Neurons in perirhinal cortex did not show this correlation.Simulations of a matched filter model match the experimental results, suggesting that area TE neurons store a synaptic memory trace during short-term visual memory.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Neuropsychology, National Institute of Mental Health, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, United States of America.

ABSTRACT
Visual short-term memory tasks depend upon both the inferior temporal cortex (ITC) and the prefrontal cortex (PFC). Activity in some neurons persists after the first (sample) stimulus is shown. This delay-period activity has been proposed as an important mechanism for working memory. In ITC neurons, intervening (nonmatching) stimuli wipe out the delay-period activity; hence, the role of ITC in memory must depend upon a different mechanism. Here, we look for a possible mechanism by contrasting memory effects in two architectonically different parts of ITC: area TE and the perirhinal cortex. We found that a large proportion (80%) of stimulus-selective neurons in area TE of macaque ITCs exhibit a memory effect during the stimulus interval. During a sequential delayed matching-to-sample task (DMS), the noise in the neuronal response to the test image was correlated with the noise in the neuronal response to the sample image. Neurons in perirhinal cortex did not show this correlation. These results led us to hypothesize that area TE contributes to short-term memory by acting as a matched filter. When the sample image appears, each TE neuron captures a static copy of its inputs by rapidly adjusting its synaptic weights to match the strength of their individual inputs. Input signals from subsequent images are multiplied by those synaptic weights, thereby computing a measure of the correlation between the past and present inputs. The total activity in area TE is sufficient to quantify the similarity between the two images. This matched filter theory provides an explanation of what is remembered, where the trace is stored, and how comparison is done across time, all without requiring delay period activity. Simulations of a matched filter model match the experimental results, suggesting that area TE neurons store a synaptic memory trace during short-term visual memory.

Show MeSH
Related in: MedlinePlus