Posterior capsulorhexis with optic capture in pediatric cataract and intraocular lens surgery

To study brain regions involved in familiarity discrimination, rats were shown sets of novel and familiar objects. On each trial two objects were shown simultaneously to a rat so that one eye saw a novel object while the other saw a familiar object. Thus novel and familiar objects were seen with the same conditions of alertness and eye movements. Activated neurones were revealed by staining for products of the immediate early gene c-fos. Familiar stimuli activated significantly fewer neurones than novel stimuli in perirhinal cortex and area TE of temporal cortex, and the ventral lateral geniculate nucleus of the thalamus, but not in the hippocampus or other areas sampled. These findings are discussed in relation to recognition memory.     

Perirhinal cortex ablation impairs visual object identification

Impairments in both recognition memory and concurrent discrimination learning have been shown to follow perirhinal cortex ablation in the monkey. The pattern of these impairments is consistent with the hypothesis that the perirhinal cortex has a role in the visual identification of objects. In this study we compared the performance of a group of three cynomolgus monkeys with bilateral perirhinal cortex ablation with that of a group of three normal controls in two tasks designed to test this hypothesis more directly. In experiment 1 the subjects relearned a set of 40 familiar concurrent discrimination problems; the stimuli in each trial were digitized images of real objects presented in one of three different views. After attaining criterion they were tested on the same problems using similar, but previously unseen, views of the objects. In experiment 2 the subjects were tested on their ability to perform 10 of these familiar discriminations with each problem presented in the unfamiliar context of a digitized image of a unique complex scene. The subjects with ablations were significantly impaired on both tasks. These results demonstrate that the role of the perirhinal cortex is not restricted to memory, and they support the hypothesis that the perirhinal cortex is involved in visual object identification. We suggest that the perirhinal cortex is crucially involved in processing coherent concepts of individual objects. A deficit of this nature could underlie the pattern of impairments that follow perirhinal cortex damage in both visual object recognition memory and visual associative memory.     

Lesions of the rat perirhinal cortex spare the acquisition of a complex configural visual discrimination yet impair object recognition.

Rats with perirhinal cortex lesions were sequentially trained in a rectangular water tank on a series of 3 visual discriminations, each between mirror-imaged stimuli. When these same discriminations were tested concurrently, the rats were forced to use a configural strategy to solve the problems effectively. There was no evidence that lesions of the perirhinal cortex disrupted the ability to learn the concurrent configural discrimination task, which required the rats to learn the precise combination of stimulus identity with stimulus placement (“structural” learning). The same rats with perirhinal cortex lesions were also unimpaired on a test of spatial working memory (reinforced T maze alternation), although they were markedly impaired on a new test of spontaneous object recognition. For the recognition test, rats received multiple trials within a single session in which on every trial, they were allowed to explore 2 objects, 1 familiar, the other novel. On the basis of their differential exploration times, rats with perirhinal cortex lesions showed very poor discrimination of the novel objects, thereby confirming the effectiveness of the surgery. The discovery that bilateral lesions of the perirhinal cortex can leave configural (structural) learning seemingly unaffected points to a need to refine those models of perirhinal cortex function that emphasize its role in representing conjunctions of stimulus features. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential neuronal encoding of novelty, familiarity and recency in regions of the anterior temporal lobe

Activity of 2072 neurones was recorded in the anterior temporal lobe--in area TE, perirhinal cortex, entorhinal cortex and hippocampus--during performance of a visual recognition task by monkeys. In area TE, perirhinal cortex and entorhinal cortex, 454 neurones (38% of the 1162 visually responsive neurones) responded differentially on the basis of the relative familiarity or recency of presentation of the stimuli; in the hippocampus only one (3%) of its 40 visually responsive neurones) did so. The differentially responsive neurones were classified into those signalling information concerning the recency (19%), familiarity (37%) or novelty (38%) of stimuli. For 98% of these neurones a decreased response signalled that stimuli had occurred previously: no large response increments were observed. The mean differential latency of each of these types of neurone was shorter (approximately 75 ms) in area TE than in the other areas. Examples of each of these types of neurone with memory spans of approximately 24 h were found in each region. The mean memory span of recency neurones was significantly longer in perirhinal cortex than area TE. For familiarity neurones a significant mean response decrement took 4-8 min to develop, indicating a slow underlying plastic change, in contrast to the rapid change seen for recency and novelty neurones. The implications of these results are discussed in relation to the neuronal basis of recognition memory.     

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.     

“I've seen it all before”: Explaining age-related impairments in object recognition. Theoretical comment on Burke et al. (2010).

Animal models are useful in elucidating the neural basis of age-related impairments in cognition. Burke, Wallace, Nematollahi, Uprety, and Barnes (2010) tested young and aged rats in several different protocols to measure object recognition memory and found that object recognition deficits in aged rats were consistent with these rats behaving as if novel objects were familiar, rather than familiar objects being treated as novel (that is, forgotten). A similar pattern of behavior has been observed in young rats with perirhinal cortex lesions. Moreover, age-related impairments in object recognition were uncorrelated with deficits in spatial learning in the water maze, a task that requires the integrity of the hippocampus and is also reliably impaired in aged rats. Taken together, these findings support functional specialization of structures within the medial temporal lobe “memory system,” as well as the independence of age-related deficits in different cognitive domains. They also potentially form a foundation for neurobiological study of age-related impairments in perirhinal cortex function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Class II correction with magnets and superelastic coils followed by straight-wire mechanotherapy. Occlusal changes during and after dental therapy

We investigated facial recognition memory (for previously unfamiliar faces) and facial expression perception with functional magnetic resonance imaging (fMRI). Eight healthy, right-handed volunteers participated. For the facial recognition task, subjects made a decision as to the familiarity of each of 50 faces (25 previously viewed; 25 novel). We detected signal increase in the right middle temporal gyrus and left prefrontal cortex during presentation of familiar faces, and in several brain regions, including bilateral posterior cingulate gyri, bilateral insulae and right middle occipital cortex during presentation of unfamiliar faces. Standard facial expressions of emotion were used as stimuli in two further tasks of facial expression perception. In the first task, subjects were presented with alternating happy and neutral faces; in the second task, subjects were presented with alternating sad and neutral faces. During presentation of happy facial expressions, we detected a signal increase predominantly in the left anterior cingulate gyrus, bilateral posterior cingulate gyri, medial frontal cortex and right supramarginal gyrus, brain regions previously implicated in visuospatial and emotion processing tasks. No brain regions showed increased signal intensity during presentation of sad facial expressions. These results provide evidence for a distinction between the neural correlates of facial recognition memory and perception of facial expression but, whilst highlighting the role of limbic structures in perception of happy facial expressions, do not allow the mapping of a distinct neural substrate for perception of sad facial expressions.     

Learning of discriminations is impaired, but generalization to altered views is intact, in monkeys (Macaca mulatta) with perirhinal cortex removal.

Rhesus monkeys (Macaca mulatta) were taught a large number of visual discriminations and then either received bilateral removal of the perirhinal cortex or were retained as unoperated controls. Operated monkeys were impaired in retention of the preoperatively learned problems. To test for generalization to novel views, the monkeys were required to discriminate, in probe trials, familiar pairs of images that were rotated, enlarged, shrunken, presented with color deleted, or degraded by masks. Although these manipulations reduced accuracy in both groups, the operated group was not differentially affected. In contrast, the same operated monkeys were impaired in reversal of familiar discriminations and in acquisition of new single-pair discriminations. These results indicate an important role for perirhinal cortex in visual learning, memory, or both, and show that under a variety of conditions, perirhinal cortex is not critical for the identification of stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pattern separation deficits may contribute to age-associated recognition impairments.

Normal aging is associated with impairments in stimulus recognition. In the current investigation, object recognition was tested in adult and aged rats with the standard spontaneous object recognition (SOR) task or two variants of this task. On the standard SOR task, adult rats showed an exploratory preference for the novel object over delays up to 24 h, whereas the aged rats only showed significant novelty discrimination at the 2-min delay. This age difference appeared to be because of the old rats behaving as if the novel object was familiar. To test this hypothesis directly, rats participated in a variant of the SOR task that allowed the exploration times between the object familiarization and the test phases to be compared, and this experiment confirmed that aged rats falsely “recognize” the novel object. A final control examined whether or not aged rats exhibited reduced motivation to explore objects. In this experiment, when the environmental context changed between familiarization and test, young and old rats failed to show an exploratory preference because both age groups spent more time exploring the familiar object. Together these findings support the view that age-related impairments in object recognition arise from old animals behaving as if novel objects are familiar, which is reminiscent of behavioral impairments in young rats with perirhinal cortical lesions. The current experiments thus suggest that alterations in the perirhinal cortex may be responsible for reducing aged animals' ability to distinguish new stimuli from ones that have been encountered previously. (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.     

The effects of neurotoxic lesions of the perirhinal cortex combined to fornix transection on object recognition memory in the rat

The effects of lesions centred in the perirhinal cortex region (Prh) or in both the perirhinal cortex region and the fornix (Prh + Fx) were assessed in two different working memory tasks, one spatial the other nonspatial. For the spatial task the rats were tested in an eight arm radial maze, using a standard procedure in which they were rewarded for avoiding previously visited arms. The Prh + Fx, but not the Prh, rats produced significantly more errors (re-entries) and these started significantly earlier in each session when compared with a surgical control group. The nonspatial task was a test of spontaneous object recognition in which rats were tested on their ability to discriminate between a familiar and a novel object. For the initial tests the Prh group failed to discriminate between the objects, but the Prh + Fx group showed a clear preference for the novel object. Observation of the test showed, however, that the Prh + Fx group were spending a greater length of time initially exploring the sample (familiar) object. When the amount of exposure to the sample object was limited to either 20 or 40 s (i.e. was the same for all three groups), the Prh + Fx group now failed to discriminate between the two objects. This change was especially evident for shorter sample duration (20 s). The Prh group did, however, show an amelioration of their deficit with this further testing. The present results support previous dissociation between spatial and nonspatial working memory, and indicate that there may be some recovery of function following perirhinal cortical damage.     

Recognition memory: neuronal substrates of the judgement of prior occurrence

Recognition memory relies on two processes: (i) identification and (ii) judgement concerning prior occurrence. A system centred on perirhinal cortex appears to be responsible for judgement of prior occurrence based on discrimination of the familiarity of stimuli or their recency of occurrence; in contrast, a hippocampal system probably supplies information concerning the episodic, contextual aspects of recognition memory. This review chiefly concerns the perirhinal system and, in particular, neurones that signal the prior occurrence of stimuli by a decrease in response. Details concerning such decremental responses are given and it is argued that such responses in perirhinal cortex are adequate for and central to discrimination of stimulus familiarity and recency in a wide range of situations. Information is given of similar types of neuronal responses in anatomically related brain regions and what may be deduced about the operation of the recognition memory system. The possibility is discussed that the neuronal responses that signal information concerning the recent occurrence of stimuli may contribute to repetition priming as well as recognition memory. Other described changes in the activity of individual neurones such as response enhancements, or sustained (delay) activity may allow solution of specialised forms of recognition memory tasks where relatively short-term working memory is adequate. Implications of the multi-faceted nature of recognition memory for the interpretation of results are emphasised. Unsolved problems and avenues for future experimentation, including determining the nature of possible underlying synaptic plastic changes, are discussed.     

Brain activity differentiates face and object processing in 6-month-old infants.

Event-related potentials were used to determine whether infants, like adults, show differences in spatial and temporal characteristics of brain activation during face and object recognition. Three aspects of visual processing were identified: (a) differentiation of face vs. object (P400 at occipital electrode was shorter latency for faces), (b) recognition of familiar identity (Nc, or negative component, at frontotemporal electrodes [FTEs] was of larger amplitude for familiar stimuli), and (c) encoding novelty (slow wave at FTEs was larger for unfamiliar stimuli). The topography of the Nc was influenced by category type: Effects of familiarity were limited to the midline and right anterior temporal electrodes for faces but extended to all temporal electrodes for objects. Results show that infants' experience with specific examples within categories and their general category knowledge influence the neural correlates of visual processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory impairment on a delayed non-matching-to-position task after lesions of the perirhinal cortex in the rat.

Previous research conducted in monkeys and rats has established that the perirhinal cortex is critically involved in object- or stimulus-recognition memory, whereas other research suggests this region may contribute to memory for object discriminations. These findings do not rule out the possibility that the perirhinal cortex plays a more general role in memory. The present experiment addressed whether selective lesions of the perirhinal cortex would result in a delay-dependent deficit on a test of memory that did not involve stimulus recognition or object memory. Rats with bilateral perirhinal lesions were tested on a delayed non-matching-to-position task. Lesions of the perirhinal cortex did not interfere with acquisition or performance at short (0–4 s)-delay intervals, but lesions did impair performance at longer delays. It is suggested that the perirhinal cortex is involved in maintaining representations of trial-specific information over time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the perirhinal cortex do not impair integration of visual and geometric information in rats.

Rats with lesions of the perirhinal cortex and a control group were required to find a platform in 1 corner of a white rectangle and in the reflection of this corner in a black rectangle. Test trials revealed that these groups were able to integrate information regarding the shape of the pool and the color of its walls (black or white) to identify the correct location of the platform. A clear effect of the perirhinal cortex lesions was, however, revealed using an object recognition task that involved the spontaneous exploration of novel objects. The results challenge the view that the perirhinal cortex enables rats to solve discriminations involving feature ambiguity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of muscarinic blockade in perirhinal cortex during visual recognition

Stimulus recognition in monkeys is severely impaired by destruction or dysfunction of the perirhinal cortex and also by systemic administration of the cholinergic-muscarinic receptor blocker, scopolamine. These two effects are shown here to be linked: Stimulus recognition was found to be significantly impaired after bilateral microinjection of scopolamine directly into the perirhinal cortex, but not after equivalent injections into the laterally adjacent visual area TE or into the dentate gyrus of the overlying hippocampal formation. The results suggest that the formation of stimulus memories depends critically on cholinergic-muscarinic activation of the perirhinal area, providing a new clue to how stimulus representations are stored.     

Familiarization, Attention, and Recognition Memory in Infancy: An Event-Related Potential and Cortical Source Localization Study.

This study investigated the effects of familiarization and attention on event-related potential (ERP) correlates of recognition memory in infants. Infants 4.5, 6, or 7.5 months of age were either familiarized with 2 stimuli that were used during later testing or presented 2 stimuli that were not used later. Then, infants were presented with a recording of Sesame Street to elicit attention or inattention and presented with familiar and novel stimuli. A negative ERP component over the frontal and central electrodes (Nc) was larger in the preexposure familiarization group for novel- than for familiar-stimulus presentations, whereas the Nc did not differ for the group not receiving a familiarization exposure. Spatial independent components analysis of the electroencephelogram and "equivalent current dipole" analysis were used to examine putative cortical sources of the ERP components. The cortical source of Nc was located in areas of prefrontal cortex and anterior cingulate cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Magnitude of the object recognition deficit associated with perirhinal cortex damage in rats: Effects of varying the lesion extent and the duration of the sample period.

The present study examines 2 factors that might moderate the object-recognition deficit seen after perirhinal cortex damage. Object recognition by normal rats was improved by extending (from 4 to 8 min) the sample period during which an object was first explored. Furthermore, there was a significant positive correlation between time spent in close exploration of the sample object and degree of successful novelty discrimination. In contrast, rats with perirhinal cortex lesions failed to benefit from increased close exploration and did not discriminate the novel object after even the longest sample period. Nevertheless, the lesions did not disrupt habituation across repeated exposure to the same object. The second factor was extent of perirhinal cortex damage. A significant correlation was found between total perirhinal cortex loss and degree of recognition impairment. Within the perirhinal cortex, only damage to the caudal perirhinal cortex correlated significantly with recognition memory deficits. This study highlights the critical importance of the perirhinal cortex within the temporal lobe for recognition memory and shows that the lesion-induced deficit occurs despite seemingly normal levels of close object exploration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perirhinal cortex ablation in rats selectively impairs object identification in a simultaneous visual comparison task.

In Experiment 1, rats discriminated among computer-generated visual displays (scenes) comprising 3 different shapes (objects). One constant scene (unrewarded) appeared on every trial together with a trial-unique variable scene (rewarded). Four types of variable scene were intermingled: (a) unfamiliar objects in different positions from the constant; (b) unfamiliar objects in same positions as the constant; (c) same objects as the constant in different positions; (d) same objects and positions, recombined. Aspiration lesions of perirhinal cortex impaired performance with type (b) only. Experiment 2 tested spatial delayed nonmatching-to-sample. The perirhinal group were impaired nonsignificantly, and less than fornix-transected rats in an earlier study. Rats' perirhinal cortex, like monkeys', subserves object identification in the absence of memory requirement but does not contribute substantially to hippocampal system spatial memory function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Role of Perirhinal Cortex in Visual Discrimination Learning for Visual Secondary Reinforcement in Rats.

Perirhinal cortex in monkeys has been thought to be involved in visual associative learning. The authors examined rats' ability to make associations between visual stimuli in a visual secondary reinforcement task. Rats learned 2-choice visual discriminations for secondary visual reinforcement. They showed significant learning of discriminations before any primary reinforcement. Following bilateral perirhinal cortex lesions, rats continued to learn visual discriminations for visual secondary reinforcement at the same rate as before surgery. Thus, this study does not support a critical role of perirhinal cortex in learning for visual secondary reinforcement. Contrasting this result with other positive results, the authors suggest that the role of perirhinal cortex is in "within-object" associations and that it plays a much lesser role in stimulus-stimulus associations between objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)