Visual Long-term Memory Research Articles

Tomita H, Ohbayashi M, Nakahara K, Hasegawa I, Miyashita Y

Knowledge or experience is voluntarily recalled from memory by reactivation of the neural representations in the cerebral association cortex. In inferior temporal cortex, which serves as the storehouse of visual long-term memory, activation of mnemonic engrams through electric stimulation results in imagery recall in humans, and neurons can be dynamically activated by the necessity for memory recall in monkeys. Neuropsychological studies and previous split-brain experiments predicted that prefrontal cortex exerts executive control upon inferior temporal cortex in memory retrieval; however, no neuronal correlate of this process has ever been detected. Here we show evidence of the top-down signal from prefrontal cortex. In the absence of bottom-up visual inputs, single inferior temporal neurons were activated by the top-down signal, which conveyed information on semantic categorization imposed by visual stimulus-stimulus association. Behavioural performance was severely impaired with loss of the top-down signal. Control experiments confirmed that the signal was transmitted not through a subcortical but through a fronto-temporal cortical pathway. Thus, feedback projections from prefrontal cortex to the posterior association cortex appear to serve the executive control of voluntary recall.

Top-down signal from prefrontal cortex in executive control of memory retrieval.

Knowledge or experience is voluntarily recalled from memory by reactivation of the neural representations in the cerebral association cortex. In inferior temporal cortex, which serves as the storehouse of visual long-term memory, activation of mnemonic engrams through electric stimulation results in imagery recall in humans, and neurons can be dynamically activated by the necessity for memory recall in monkeys. Neuropsychological studies and previous split-brain experiments predicted that prefrontal cortex exerts executive control upon inferior temporal cortex in memory retrieval; however, no neuronal correlate of this process has ever been detected. Here we show evidence of the top-down signal from prefrontal cortex. In the absence of bottom-up visual inputs, single inferior temporal neurons were activated by the top-down signal, which conveyed information on semantic categorization imposed by visual stimulus-stimulus association. Behavioural performance was severely impaired with loss of the top-down signal. Control experiments confirmed that the signal was transmitted not through a subcortical but through a fronto-temporal cortical pathway. Thus, feedback projections from prefrontal cortex to the posterior association cortex appear to serve the executive control of voluntary recall.

Cognitive profile of patients with relapsing remitting multiple sclerosis.

Multiple sclerosis (MS) is a common disease in Western countries of temperate/cold climate, but in tropical countries an increasing number of cases have been diagnosticated. Moved by the lack of information about cognitive dysfunction of Brazilian MS patients, the present study attempted to describe features of neuropsychological alterations in patients with relapsing remitting MS living in the city of São Paulo. They were compared to healthy volunteers, matched for age and education. In the absence of global intellectual deterioration, the patients had a deficit: a) in learning and verbal long-term memory tasks and in visual long-term memory of complex figure; b) in timed tasks, accounted for by a slowness of mental processes; c) in tasks with a motor component. Tendency to depression was observed; anxiety levels were normal.

Coexistence of uncorrelated and correlated attractors in a nonmonotonic neural network

A neural network with correlated attractors ala Griniasty et al (1993 Conversion of temporal correlations between stimuli to spatial correlations between attractors Neural Comp. 5 1-17) is studied for a nonmonotonic response function in the cases of both finite and extensive memory loading. In the finite loading case with symmetric synaptic connections, the number of neighbouring memory patterns correlated with an attractor tends to be decreased as the degree of nonmonotonicity is increased. To study the extensive loading case, we generalize the previously proposed self-consistent signal-to-noise analysis to associative memory models with a general class of local Hebbian synaptic connections. Applying the results to the present model, we derive analytic expressions for the equilibrium order parameters. New finding includes the coexistence of uncorrelated and correlated attractors in the obtained phase diagram. This fact, which is confirmed by extensive numerical simulations, may have significant implications for long-term visual memory.

Episodic memory and learning in patients with chronic schizophrenia

This study explored the pattern of memory functioning in 58 patients with chronic schizophrenia and compared their performance with 53 normal controls. Multiple domains of memory were assessed, including verbal and non-verbal memory span, verbal and non-verbal paired associate learning, verbal and visual long-term memory, spatial and non-spatial conditional associative learning, recognition memory and memory for temporal order. Consistent with previous studies, substantial deficits in long-term memory were observed, with relative preservation of memory span. Memory for temporal order and recognition memory was intact, although significant deficits were observed on the conditional associative learning tasks. There was no evidence of lateralized memory impairment. In these respects, the pattern of memory impairment in schizophrenia is more similar in nature to that found in patients with memory dysfunction following mesiotemporal lobe lesions, rather than that associated with focal frontal lobe damage.

Callosal window between prefrontal cortices: cognitive interaction to retrieve long-term memory.

A perceptual image can be recalled from memory without sensory stimulation. However, the neural origin of memory retrieval remains unsettled. To examine whether memory retrieval can be regulated by top-down processes originating from the prefrontal cortex, a visual associative memory task was introduced into the partial split-brain paradigm in monkeys. Long-term memory acquired through stimulus-stimulus association did not transfer via the anterior corpus callosum, a key part interconnecting prefrontal cortices. Nonetheless, when a visual cue was presented to one hemisphere, the anterior callosum could instruct the other hemisphere to retrieve the correct stimulus specified by the cue. Thus, although visual long-term memory is stored in the temporal cortex, memory retrieval is under the executive control of the prefrontal cortex.

Visual memory-deficit amnesia: a distinct amnesic presentation and etiology.

We describe a form of amnesia, which we have called visual memory-deficit amnesia, that is caused by damage to areas of the visual system that store visual information. Because it is caused by a deficit in access to stored visual material and not by an impaired ability to encode or retrieve new material, it has the otherwise infrequent properties of a more severe retrograde than anterograde amnesia with no temporal gradient in the retrograde amnesia. Of the 11 cases of long-term visual memory loss found in the literature, all had amnesia extending beyond a loss of visual memory, often including a near total loss of pretraumatic episodic memory. Of the 6 cases in which both the severity of retrograde and anterograde amnesia and the temporal gradient of the retrograde amnesia were noted, 4 had a more severe retrograde amnesia with no temporal gradient and 2 had a less severe retrograde amnesia with a temporal gradient.

Spatial frequency discrimination: Visual long-term memory or criterion setting?

A long-term sensory memory is believed to account for spatial frequency discrimination when reference and test stimuli are separated by long intervals. We test an alternative proposal: that discrimination is determined by the range of test stimuli, through their entrainment of criterion-setting processes. Experiments 1 and 2 show that the 50% point of the psychometric function is largely determined by the midpoint of the stimulus range, not by the reference stimulus. Experiment 3 shows that discrimination of spatial frequencies is similarly affected by orthogonal contextual stimuli and parallel contextual stimuli and that these effects can be explained by criterion-setting processes. These findings support the hypothesis that discrimination over long intervals is explained by the operation of criterion-setting processes rather than by long-term sensory retention of a neural representation of the stimulus.

The neuronal basis of visual memory and imagery in the primate: A neurophysiological approach

To understand the biological basis of memory is one of the most exciting frontiers of science. Single unit recording is a powerful method to investigate neuronal correlates of various brain functions such as memory in awake animals. Anatomical, neuropsychological, and neurophysiological evidence indicates that the IT has an important role not only for synthesizing the analyzed visual attribute into a unique configuration, but also for the storehouse of visual memory in humans and primates. We performed single unit recordings in the primate IT, and found neuronal correlates of visual long-term memory: the IT neurons could reflect learned associative relations among stimuli. The findings reviewed here support the hypothesis that the IT is a region of the brain where visual perception meets memory and imagery.

The neuronal basis of visual memory and imagery in the primate: A neurophysiological approach

To understand the biological basis of memory is one of the most exciting frontiers of science. Single unit recording is a powerful method to investigate neuronal correlates of various brain functions such as memory in awake animals. Anatomical, neuropsychological, and neurophysiological evidence indicates that the IT has an important role not only for synthesizing the analyzed visual attribute into a unique configuration, but also for the storehouse of visual memory in humans and primates. We performed single unit recordings in the primate IT, and found neuronal correlates of visual long-term memory: the IT neurons could reflect learned associative relations among stimuli. The findings reviewed here support the hypothesis that the IT is a region of the brain where visual perception meets memory and imagery.

Positron-emission tomography imaging of long-term shape recognition challenges.

Long-term visual memory performance was impaired by two types of challenges: a diazepam challenge on acquisition and a sensory challenge on recognition. Using positron-emission tomography regional cerebral blood flow imaging, we studied the effect of these challenges on regional brain activation during the delayed recognition of abstract visual shapes as compared with a baseline fixation task. Both challenges induced a significant decrease in differential activation in the left fusiform gyrus, suggesting that this region is involved in the automatic or volitional comparison of incoming and stored stimuli. In contrast, thalamic differential activation increased in response to memory challenges. This increase might reflect enhanced retrieval attempts as a compensatory mechanism for restoring recognition performance.

The representation of color and form in long-term memory

Color and form are elementary stimulus encoding dimensions that have effects on the representation of visual stimuli at early processing stages. Little is known, however, about their effects on visual long-term memory. In three experiments we investigated whether color is part of the memory representation, whether color and form are bound in the memory representation, and the effect of color context on memory performance. Experimental results suggest that color is part of the memory representation and that color and form can be represented separately in memory and accessed independently. We suggest that the binding of color and form is a deliberate strategic act that requires focal attention, not a natural consequence of processing visual stimuli. We compare our results with the predictions of two computational memory models regarding feature binding. The effect of color context was not straightforward; however, results are consistent with the encoding specificity principle.

Activity of primate inferotemporal neurons related to a sought target in pair-association task.

Visual long-term memory in primates has been assessed by using the pair-association (PA) task, in which a subject retrieves and chooses the paired associate of a cue picture. Our previous studies on single neurons in the anterior inferotemporal (AIT) cortex suggested their roles in representing paired associates in the mind. To test the possibility that the delay activity of AIT neurons is related to a particular picture as a sought target, we devised the PA with color switch (PACS) task. In the PACS task, the necessity for memory retrieval and its initiation time were controlled by a color switch in the middle of the delay period. A control task, in which there is no color switch, corresponds to the conventional delayed matching-to-sample (DMS) task where the monkey chooses the same picture as a cue. We found that AIT neurons started to respond just after the color switch in the PACS task, when the cue-optimal picture's associate was presented as a cue. In contrast, they showed no response change in the DMS task. We confirmed that this effect is not due to the visual response to colors. Furthermore, when the cue-optimal picture was presented as a cue, these neurons showed suppression after the color switch in the PACS task. These results suggest that the activity of AIT neurons mediates gating mechanisms that preferentially pass information about a sought target, even when the sought target is retrieved from long-term memory.

視空間スケッチパッドへの長期記憶の影響 新近性効果の新たな要因の検討

Three immediate serial recall experiments, using articulatory suppression examined the influence of visual long-term memory on visuo-spatial sketchpad. In Experiments 1 and 2, serial recall rates of unfamiliar figures, familiar figures, and numbers were investigated. The results showed that the more visual long-term memory the stimuli evoked, the more salient recency effects and primacy effects occurred. Based on these results, the following process is hypothesized to be one of the factors causing recency effects. If the visual information of items inputted into visuo-spatial sketchpad is already in long-term memory, only their retrieval cues are formed and retained. Thus, other information is erased from visuo-spatial sketchpad, which makes more room, so that subsequent items are inputted into visuo-spatial sketchpad. In Experiment 3, reaction times of a visual secondary task during presentation were measured. The results indicated that there was more room in visuo-spatial sketchpad when primacy and recency effects occurred, which supported the hypothesis. Finally, the interaction of working memory and long-term memory is discussed.

Two types of representation in visual memory: Evidence from the effects of stimulus contrast on image combination

An imagery task was used to explore the distinction between visual memory representations that preserve surface features and more abstract descriptions. Subjects were shown two line drawings and were then asked to combine a visual image of each drawing in order to identify a novel figure. The main experimental manipulation concerned the contrast in which each drawing was shown, which was either normal or reversed. Experiment 1 showed that image combination was more efficient when the contrasts of the two drawings were congruent with each other, but only when the imagery task was performed under conditions emphasizing short-term memory (STM). There was no effect of congruity when one of the images was generated from long-term memory (LTM). These results are consistent with the idea that the surface characteristics of a stimulus are preserved in visual STM, but a more abstract description is stored in visual LTM. In Experiment 2 we explored the influence of verbal recoding on performance of the imagery task by requiring subjects to suppress articulation. Under LTM conditions, performance of the imagery task was improved by suppression and became sensitive to contrast congruity. Under STM conditions, imagery was unaffected by suppression. Overall, these results support the distinction between surface and abstract descriptions in visual memory. However, they suggest that this distinction does not map onto that between STM and LTM in any simple way. It is suggested that short-term visual memory maintains surface descriptions and long-term visual memory preserves both surface and abstract descriptions. Verbal coding of visual stimuli appears to encourage the use of abstract visual descriptions.

High-Fidelity Perceptual Long-Term Memory

Visual long-term memory for spatial information was assessed by measuring discrimination thresholds for the spatial frequency of sinusoidal gratings in a delayed discrimination task, with various time intervals separating test and reference stimuli The results demonstrate perfect preservation of information across 1-s to 50-hr retention intervals in the sense that the spatial frequency discrimination thresholds remained at the level defined by the spatial resolution of the sensory analysis This high-fidelity spatial long-term memory may represent an elementary memory mechanism for precategoncal storage of visual features

Mnestic disorders in long-term high-dose diazepam abuse: a pilot study

SummaryCognitive impairment in long-term high-dose diazepam abusers (dose > 30 mg diazepam/day; duration of abuse > 12 months) was examined by administering four memory-related tests and comparing the outcomes with those of matched controls. Deficits were found in spatial and visual learning, spatial and visual short-term memory (STM) as well as for spatial and visual long-term memory (LTM). As for verbal aspects of memory, solely the acquisition of novel verbal material (verbal learning) was impaired, Furthermore, deficits in a concentration task were observed. In chronic abuse the established memory deficits are similar to cognitive impairment after single doses. Relaxing or anxiety-reducing effects of diazepam were no longer present. The results of this experimental study demonstrate the risks of diazepam use beyond therapeutic range.

The effects of number of stimuli and prior exposure on performance of concurrent visual discriminations during suppression of inferotemporal cortex with cold.

The visual part of the temporal cortex, cytoarchitectural area TE has been split into dorsal (TEd) and ventral (TEv) subdivisions. TE has long been associated with the identification of objects. However, in order to explain retrieval deficits with suppression of prestriate cortex, but not with suppression of TE, we hypothesized that object identification might take place in a working memory in the prestriate cortex upstream from TE. Exposure to the stimuli before suppressing TEd was hypothesized to cause its contribution to be relayed to prestriate cortex in anticipation of further work with them. This predicts that during TEd suppression there is a loss of access to some long-term visual memory, and without that access, large numbers of stimuli should overwhelm the limited capacity working memory. It also predicts that prior exposure to stimuli should protect them from loss during TEd suppression. We challenged these predictions in two experiments. In the first, we tested the animals on three concurrent discriminations requiring them to retrieve 8 pairs of stimuli for each one. The animals performed well on some of the discriminations during TEd suppression, but failed on others, which is consistent with the prediction. Also, different animals failed with different stimuli. However, when we tested with only the failed discriminations, they still did badly with one or two pairs, which is not consistent with the prediction. In the second experiment, we tested them with 1, 4, 7 or 10 pairs of visual discriminations drawn from a set of 23 the animals had learned. Half of the discriminations were presented immediately before suppression and half were not.(ABSTRACT TRUNCATED AT 250 WORDS)

Visual object agnosia, prosopagnosia, achromatopsia, loss of visual imagery, and autobiographical amnesia following recovery from cortical blindness: Case M.H.

A number of higher visual deficits accompanied by severe retrograde autobiographical memory loss following bilateral medial occipital infarctions are described in case M.H. Assessment of M.H.'s visual object agnosia and prospagnosia suggested that he was unable to integrate the elements of a percept to form a meaningful whole. This deficit may occur at the level the percept is encoded into the visual buffer and inspected. M.H. also describes a loss of visual memories, and it is hypothesized that this may similarly be a result of an inability to integrate the elements of the visual representation (e.g. of an object or face) following its generation from long-term visual memory store into the visual buffer. M.H.'s retrograde autobiographical memory loss is postulated to be a consequence of the severe impoverishment of episodic memories that must occur when events originally stored multimodally, must be recalled without any visual component.

Inferior temporal cortex: where visual perception meets memory.

The neural processes that lead to visual perception and memory, thus subserving the identification of objects, have been assigned to the multi­ synaptic occipito-temporo-limbic projection that interconnects the striate, prestriate, inferior temporal, and hippocampal cortices (Gross 1972; Maunsell & Newsome 1987; Mishkin et al 1983). Recent advances in our understanding of the organization of the extra striate cortex revealed a mosaic of more than 25 visual areas beyond the striate cortex (Felleman & Van Essen 1991; Van Essen 1985; Zeki & Shipp 1988). The physical properties of a visuaJ object (such as its size, color, texture, and shape) are analyzed in the multiple subdivisions of the prestriate-posterior temporal complex. The anterior part of inferior temporal cortex has been hypo­ thesized not only to synthesize the analyzed attributes into a unique con­ figuration, but also to work as the storehouse for central representations of the objects (Mishkin 1982; Weiskrantz & Saunders 1984). The supporting evidence for this hypothesis has mainly been given by neuropsychological approaches (Milner 1990; Squire & Zola-Morgan 1991; Weiskrantz 1990). Recently, neuronal correlates of the visual long-term memory were found: The temporal-lobe neurons could reflect learned associative relations among stimuli (Miyashita 1988; Sakai & Miyashita 1991). The findings on this associational mechanism, together with that on the feature selectivity