Selective effects of triazolam on memory for emotional, relative to neutral, stimuli: Differential effects on gist versus detail.

Benzodiazepines are known to reduce learning and memory performance, presumably through their facilitation of GABAergic neurotransmission, but the effects of these drugs specifically on memory for emotional material has not been addressed in humans. The effects of a benzodiazepine (triazolam, 0.25 mg) on nonincidental memory for emotional stimuli were assessed in 20 healthy volunteers (10 female). Triazolam reduced the normally facilitative effect of emotion on memory. The drug specifically affected memory for the gist of stimuli while leaving detail memory relatively unaffected. This pattern of performance is similar to that seen in patients with amygdala damage. Results suggest an effect of GABAergic neurotransmission at the level of the amygdala on memory modulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for preserved emotional memory in normal older persons.

Emotion has been shown to have a modulatory effect on declarative memory. Normal aging is associated with a decline in declarative memory, but whether aging might affect the influence of emotion on memory has not been established. To investigate this, we administered a task that provides a detailed assessment of emotional memory to 80 neurologically normal adults ranging in age from 35 to 85 years. Across ages, memory performance was found to be modulated by the emotional significance of stimuli in a comparable manner (improved memory for gist, compromised memory for visual detail), despite an overall decline in memory performance with increasing age. The results raise the interesting possibility that aging has a differential effect on hippocampal versus amygdala function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anteromedial Temporal Lobe Damage Blocks Startle Modulation by Fear and Disgust.

The acoustic startle reflex (ASR) is potentiated during negative emotion, but attenuated during positive emotional experience. The modulation of the ASR by fear depends critically on the amygdala. The authors investigated ASR modulation to fearful, disgusting, pleasant, and neutral stimuli in 12 patients with unilateral damage to the anteromedial temporal lobe including the amygdala (6 left, 6 right), 1 patient with bilateral temporal lobe damage including the amygdala, and 12 comparison participants. Both groups with unilateral damage, as well as the subject with bilateral damage, showed a complete lack of ASR potentiation to both fear and disgust stimuli. The findings suggest that potentiation of the ASR by disgust and fear depends on the integrity of the anteromedial temporal lobe. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction of frontal and perirhinal cortices in visual object recognition memory in monkeys

Monkeys were trained preoperatively in visual object recognition memory. The task was delayed matching-to-sample with lists of trial-unique randomly generated visual stimuli in an automated apparatus, and the stimuli were 2D visual objects made from randomly generated coloured shapes. We then examined the effect of either: (i) disconnecting the frontal cortex in one hemisphere from the perirhinal cortex in the contralateral hemisphere by crossed unilateral ablations; (ii) disconnecting the magnocellular portion of the mediodorsal (MDmc) thalamic nucleus in one hemisphere from the perirhinal cortex in the contralateral hemisphere; or (iii) bilaterally ablating first the amygdala, then adding fornix transection, then finally perirhinal cortex ablation. We found that both frontal/perirhinal and MDmc/perirhinal disconnection had a large effect on visual object recognition memory, whereas both amygdalectomy and the addition of fornix transection had only a mild effect. We conclude that the frontal lobe needs to interact with the perirhinal cortex within the same hemisphere for visual object recognition memory, but that routes through the amygdala and hippocampus are not of primary importance.     

Interaction of the amygdala with the frontal lobe in reward memory

Five cynomolgus monkeys (Macaca fascicularis) were assessed for their ability to associate visual stimuli with food reward. They learned a series of new two-choice visual discriminations between coloured patterns displayed on a touch-sensitive monitor screen; the feedback for correct choice was delivery of food. Normal learning in this task is known to be dependent on the amygdala. The monkeys received brain lesions which were designed to disconnect the amygdala from interaction with other brain structures thought to be involved in this memory task. All the monkeys received an amygdalectomy in one hemisphere and lesions in the other hemisphere of some of the projection targets of the amygdala, namely the ventral striatum, the mediodorsal thalamus and the ventromedial prefrontal cortex. The rate of learning new problems was assessed before and after each operation. Disconnection of the amygdala from the ventral striatum was without effect on learning rate. An earlier study had shown that disconnection of the amygdala from either the mediodorsal thalamus or the ventromedial prefrontal cortex produced only a mild impairment, significantly less severe than that produced by bilateral lesions of any of these three structures. The present results show, however, that disconnection of the amygdala from both the mediodorsal thalamus and the ventromedial prefrontal cortex in the same animal, by crossed unilateral lesions of the amygdala in one hemisphere and of both the mediodorsal thalamus and the ventromedial prefrontal cortex in the other hemisphere, produces an impairment as severe as that which follows bilateral lesions of any of these three structures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bilateral stimulus presentation in memory scanning.

24 18–40 yr olds performed a memory-scanning task (S. Sternberg, 1966, 1969) in which probe letters were displayed unilaterally or bilaterally after sets of 2, 4, or 6 letters were memorized. The mean response time (RT) to bilateral presentations was significantly longer than the mean RT to unilateral presentations, but the slope of the set-size function was not affected, suggesting that presenting stimuli bilaterally affected stages other than memory scanning. There were no significant visual-field effects in either the bilateral or unilateral conditions, suggesting that memory scanning is not a lateralized process. There was no evidence that bilateral presentation increased visual-field differences. This is not consistent with D. B. Boles' (1983, 1990) hypothesis that visual-field asymmetry effects are more pronounced with bilateral than with unilateral presentation of stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Failing to Get the Gist: Reduced False Recognition of Semantic Associates in Semantic Dementia.

In 2 experiments involving patients with semantic dementia, the authors investigated the impact of semantic memory loss on both true and false recognition. Experiment 1 involved recognition memory for categories of everyday objects that shared a predominantly semantic relationship. The patients showed preserved item-specific recollection for the pictorial stimuli but, compared with control participants, exhibited significantly reduced utilization of gist information regarding the categories of objects. The latter result is consistent with the patients' degraded semantic knowledge. Experiment 2 involved categories of abstract objects that were related to one another perceptually rather than semantically. Patients with semantic dementia obtained item-specific recollection and gist memory scores that were indistinguishable from those of control participants. These results suggest that the reduction in gist memory in semantic dementia is largely specific to semantic representations and cannot be attributed to general difficulty with abstracting and/or utilizing gistlike commonalities between stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective neurotoxic amygdala lesions in monkeys disrupt reactivity to food and object stimuli and have limited effects on memory.

Monkeys with bilateral neurotoxic amygdala lesions and normal monkeys were administered tests of emotional reactivity, recognition memory, and reward association memory. There were 3 main findings. First, monkeys with amygdala lesions performed differently than normal monkeys on initial administrations of the emotional reactivity tests and on retests that were given 21-23 months after surgery. Second, they performed like normal monkeys on tests of recognition memory. Third, they were initially impaired on a test of reward association memory, but they were not impaired on a retest that was given 16 months after surgery. These findings underscore the role of the amygdala in aspects of emotional reactivity and reward association memory, but not in recognition memory. In addition, at least some of the behavioral effects of amygdala damage can be long lasting. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Redundancy gain in the acallosal brain.

The authors measured simple reaction time (RT) to visual stimuli, presented either singly to 1 or the other visual field or in bilaterally presented pairs, to 2 women with callosal agenesis. The stimuli were either white against a black background or gray against an equiluminant yellow background. RTs to bilateral pairs were decreased beyond predictions based on a simple race between independent unilateral processes, implying interhemispheric neural summation. This effect was enhanced under equiluminance in the participant M.M. whose anterior commissure was within normal limits, but not in the participant J.P. whose anterior commissure was enlarged. The anterior commissure may act, relative to its size, to inhibit cortical activation to bilateral pairs, which then acts to decrease subcortical neural summation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recovery of sensorimotor function after frontal cortex damage in rats: Evidence that the serial lesion effect is due to serial recovery.

[Correction Notice: An erratum for this article was reported in Vol 103(1) of Behavioral Neuroscience (see record 2008-10623-002). The plate for this article appears on page 996. The information should read, "Plate B. Photographs of the dorsal side of the brains showing the minimum (top) and maximum (bottom) extent of the lesion produced unilaterally in the sham group (left) and bilaterally in the single- and two-stage groups (right)."] Multiple-staged brain lesions produce fewer and smaller behavioral effects than single surgery (the serial lesion effect, SLE). Two hypotheses were tested: the reduced deficit hypothesis and the serial recovery hypothesis. Effects of lesions of the medial frontal cortex on sensorimotor behavior were investigated in 7 rats that received bilateral damage in single surgery, 16 in 2 unilateral stages separated by 3 wks, or 5 with unilateral damage followed 3 wks later by sham surgery. Unilateral damage produced deficits on the contralateral side in response to visual, tactile, and olfactory stimuli and impairments in roll-over and paw withdrawal responses. All impairments except visual placement recovered over the next 3 wks. A 2nd unilateral lesion on the contralateral side produced the same symptoms on the opposite side. Bilateral damage incurred in a single stage produced the same deficits on both sides. Because the effects of the 2nd unilateral lesion in the 2-stage group produced comparable contralateral effects to those produced in the single-stage group, but no reinstatement of ipsilateral deficits, the reduced deficit hypothesis was rejected. It was concluded that SLE occurred as a result of serial recovery of the deficits. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Partial disruption of fear conditioning in rats with unilateral amygdala damage: correspondence with unilateral temporal lobectomy in humans

Conditioned fear in rats was assessed for the effects of pretraining amygdala lesions (unilateral vs. bilateral) across unconditioned stimulus (US) modalities (white noise vs. shock). In contrast to sham controls, unilateral amygdala lesions significantly reduced conditioned freezing responses, whereas bilateral amygdala lesions resulted in a nearly complete lack of freezing to both the conditioned stimulus (CS) and the context. The lesion effects were more pronounced for CS conditioning but were consistent across US modalities. It was concluded that white noise can serve as an effective US and that unilateral amygdala lesions attenuate but do not eliminate conditioned fear in rats. The results support our interpretation of a recent fear conditioning study in humans (K. S. LaBar, J. E. LeDoux, D. D. Spencer, & E. A. Phelps, 1995).     

Memory for gist and detail information in Alzheimer's disease and mild cognitive impairment.

Two experiments examined different forms of gist and detail memory in people with Alzheimer's disease (AD) and those with amnestic mild cognitive impairment (MCI). In Experiment 1, 14 AD, 14 MCI, and 22 control participants were assessed with the Deese-Roediger-McDermott paradigm. Results indicated that false recognition of nonstudied critical lures (gist memory) was diminished in the AD compared with the MCI and control groups; the two latter cohorts performed similarly. In Experiment 2, 14 AD, 20 MCI, and 26 control participants were tested on a text memory task. Results revealed that recall of both macropropositions (gist information) and micropropositions (detail information) decreased significantly in AD and in MCI as compared with control participants. This experiment also revealed that the impairment was comparable between gist and detail memory. In summary, the results were consistent across experiments in the AD but not in the MCI participants. The discrepancy in MCI participants might be explained by differences in the degree of sensitivity of the experimental procedures and/or by the differences in the cognitive processes these procedures assessed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amygdalar Lateralization in Fear Conditioning: Evidence for Greater Involvement of the Right Amygdala.

The relative contribution of left and right amygdalae in the acquisition and retention of fear conditioning was investigated in rats. Pretraining bilateral electrolytic lesions blocked the acquisition of conditioned fear to tone and context, whereas unilateral lesions induced partial impairments with no left-right amygdala differences. In contrast, posttraining bilateral and unilateral lesions produced significant deficits in the retention of conditioned fear to tone and context. Although no left-right difference was observed to tone, the right amygdala lesions generated greater deficits in contextual fear than the left amygdala lesions. These results indicate that fear conditioning is partially disrupted with unilateral amygdalar lesions, but that the right amygdala has greater involvement than the left amygdala when conditioning occurs under a normal brain state. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of emotional responses in monkeys with rhinal cortex or amygdala lesions.

Four emotionally arousing stimuli were used to probe the behavior of monkeys with bilateral ablations of the entorhinal and perirhinal cortex. The monkeys' behavioral changes were then contrasted with those observed earlier (M. Meunier, J. Bachevalier, E. A. Murray, L. Málková, & M. Mishkin, 1999) in monkeys with either neurotoxic or aspiration lesions of the neighboring amygdala. Rhinal cortex ablations yielded several subtle behavioral changes but none of them resembled any of the disorders typically seen after amygdalectomies. The changes produced by rhinal damage took mainly the form of heightened defensiveness and attenuated submission and approach responses, that is, just the opposite of some of the most distinctive symptoms following amygdala damage. These findings raise the possibility that the rhinal cortex and amygdala have distinct, interactive functions in normal behavioral adaptation to affective stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhinal cortex lesions produce mild deficits in visual discrimination learning for an auditory secondary reinforcer in rhesus monkeys.

Aspiration, but not neurotoxic, lesions of the amygdala impair performance on a visual discrimination learning task in which an auditory secondary reinforcer signals which of 2 stimuli will be reinforced with food. Because aspiration lesions of the amygdala interrupt projections of the rhinal cortex traveling close to the amygdala, it was hypothesized that damage to the rhinal cortex would severely impair learning in this task. Rhesus monkeys (Macaca mulatta) were trained to solve visual discrimination problems based on an auditory secondary reinforcer, were given lesions of the rhinal cortex or the perirhinal cortex alone, and were then retested. The monkeys displayed a reliable, albeit mild, deficit in postoperative performance. It is concluded that the aspiration lesions of the amygdala that produced a severe impairment did so because they interrupted connections of temporal cortical fields beyond the rhinal cortex that are also involved in learning in this task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mirror-image matching and mental rotation problem solving by baboons (Papio papio): Unilateral input enhances performance.

Three experiments, using a matching-to-sample procedure, were conducted to examine hemispheric specialization in mirror-image discrimination and mental rotation in baboons. In Exp 1, no significant difference was found in discrimination of mirror-image and asymmetric pattern stimuli. In Exp 2, orientation was assessed within the left (LVF) and right (RVF) visual half-fields. An RVF advantage was found in accuracy for asymmetric patterns, whereas an LVF advantage was found for discrimination of mirror-image stimuli. No significant relation was found between angular disparity of the stimuli and response time. Exp 3 examined the effect of bilateral visual input on accuracy and response time. Significantly lower accuracy and longer response times were found for bilateral compared with unilateral visual input. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Recovery of sensorimotor function after frontal cortex damage in rats: Evidence that the serial lesion effect is due to serial recovery": Correction.

Reports an error in "Recovery of sensorimotor function after frontal cortex damage in rats: Evidence that the serial lesion effect is due to serial recovery" by John M. de Castro and Mark C. Zrull (Behavioral Neuroscience, 1988[Dec], Vol 102[6], 843-851). The plate for this article appears on page 996. The information should read, "Plate B. Photographs of the dorsal side of the brains showing the minimum (top) and maximum (bottom) extent of the lesion produced unilaterally in the sham group (left) and bilaterally in the single- and two-stage groups (right)." (The following abstract of the original article appeared in record 1989-28759-001.) Multiple-staged brain lesions produce fewer and smaller behavioral effects than single surgery (the serial lesion effect, SLE). Two hypotheses were tested: the reduced deficit hypothesis and the serial recovery hypothesis. Effects of lesions of the medial frontal cortex on sensorimotor behavior were investigated in 7 rats that received bilateral damage in single surgery, 16 in 2 unilateral stages separated by 3 wks, or 5 with unilateral damage followed 3 wks later by sham surgery. Unilateral damage produced deficits on the contralateral side in response to visual, tactile, and olfactory stimuli and impairments in roll-over and paw withdrawal responses. All impairments except visual placement recovered over the next 3 wks. A 2nd unilateral lesion on the contralateral side produced the same symptoms on the opposite side. Bilateral damage incurred in a single stage produced the same deficits on both sides. Because the effects of the 2nd unilateral lesion in the 2-stage group produced comparable contralateral effects to those produced in the single-stage group, but no reinstatement of ipsilateral deficits, the reduced deficit hypothesis was rejected. It was concluded that SLE occurred as a result of serial recovery of the deficits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Von Restorff effect in visual object recognition memory in humans and monkeys. The role of frontal/perirhinal interaction

This study reports the development of a new, modified delayed matching to sample (DMS) visual recognition memory task that controls the relative novelty of test stimuli and can be used in human and nonhuman primates. We report findings from normal humans and unoperated monkeys, as well as three groups of operated monkeys. In the study phase of this modified paradigm, subjects studied lists of two-dimensional visual object stimuli. In the test phase each studied object was presented again, now paired with a new stimulus (a foil), and the subject had to choose the studied item. In some lists one study item (the novel or isolate item) and its associated foil differed from the others (the homogenous items) along one stimulus dimension (color). The critical experimental measure was the comparison of the visual object recognition error rates for isolate and homogenous test items. This task was initially administered to human subjects and unoperated monkeys. Error rates for both groups were reliably lower for isolate than for homogenous stimuli in the same list position (the von Restorff effect). The task was then administered to three groups of monkeys who had selective brain lesions. Monkeys with bilateral lesions of the amygdata and fornix, two structures that have been proposed to play a role in novelty and memory encoding, were similar to normal monkeys in their performance on this task. Two further groups--with disconnection lesions of the perirhinal cortex and either the prefrontal cortex or the magnocellular mediodorsal thalamus--showed no evidence of a von Restorff effect. These findings are not consistent with previous proposals that the hippocampus and amygdala constitute a general novelty processing network. Instead, the results support an interaction between the perirhinal and frontal cortices in the processing of certain kinds of novel information that support visual object recognition memory.     

Removal of the amygdala plus subjacent cortex disrupts the retention of both intramodal and cross modal associative memories in monkeys.

Naive rhesus monkeys (Macaca mulatta) were trained preoperatively in an automated test apparatus on an auditory–visual (crossmodal) conditional task or on a visual–visual (intramodal) conditional task that involved learning a fixed set of stimulus–stimulus associations or paired associates. After having learned their respective tasks, each monkey received bilateral removal of the amygdala plus subjacent cortex. The 2 experimental groups showed equally poor retention of the stimulus–stimulus associations and subsequently relearned their respective crossmodal and intramodal associations at the same rate. These data argue against the idea that the amygdala is specialized for crossmodal associations. Instead, the data indicate that the amygdala and/or its underlying cortex play a more generalized role in stimulus–stimulus associative memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sensorimotor syndrome produced by lesions of the amygdala and lateral hypothalamus.

Experimented with 7 male Long-Evans hooded rats. Small unilateral lesions of the amygdala, lateral hypothalamus, or nearby structures resulted in an inability to orient and localize, by an appropriate movement of the head, stimuli in the contralateral visual and somatosensory fields. This is neither a primary sensory nor motor deficit. Conditioning experiments revealed that the linkage between contralateral sensory and motor fields has been disrupted, possibly reflecting damage to fibers which connect sensory and motor areas within a hemisphere. This sensorimotor syndrome can account for the placidity and decreased aggressive, social, and feeding behaviors commonly observed following lesions of these areas. (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)