Role of the hippocampus plus subjacent cortex but not amygdala in visuomotor conditional learning in Rhesus monkeys.

Rhesus monkeys were trained to learn a large series of visuomotor conditional associations, each involving the arbitrary coupling of a visual stimulus with 1 of 3 potentially correct forelimb movements. The monkeys then received bilateral aspiration lesions of either the amygdala plus subjacent cortex or the hippocampus plus subjacent cortex. Hippocampal but not amygdala removals significantly retarded the learning of new visuomotor associations. Neither lesion affected retention. The findings argue against a general role for the amygdala in associating information across modalities, construed broadly to include motor information. By contrast, the finding that the hippocampal formation and its subjacent cortex play a role in learning new sensorimotor associations supports the view that this region participates in the long-term storage of associative information or in the recall of recently acquired information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Activity in the parietal area during visuomotor learning with optical rotation

Regional cerebral blood flow (rCBF) was measured in six subjects to study changes of activity in the parietal cortex during learning of a visually guided pointing task with a discrepancy of visuomotor coordination and to determine whether reorganization affects the parietal activity after learning. During the early stage of learning, the right posterior parietal cortex showed a significant increase in rCBF. During the late stage, on the other hand, significant activation was noted in the postcentral gyrus of the right hemisphere. These results support a role for the posterior parietal cortex in remapping visuomotor coordinates and suggest the involvement of the human postcentral gyrus in retaining sensorimotor coordinates, considered to relate to the self image of the hand.     

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)     

Mnemonic neuronal activity in somatosensory cortex

Single-unit activity was recorded from the hand areas of the somatosensory cortex of monkeys trained to perform a haptic delayed matching to sample task with objects of identical dimensions but different surface features. During the memory retention period of the task (delay), many units showed sustained firing frequency change, either excitation or inhibition. In some cases, firing during that period was significantly higher after one sample object than after another. These observations indicate the participation of somatosensory neurons not only in the perception but in the short-term memory of tactile stimuli. Neurons most directly implicated in tactile memory are (i) those with object-selective delay activity, (ii) those with nondifferential delay activity but without activity related to preparation for movement, and (iii) those with delay activity in the haptic-haptic delayed matching task but no such activity in a control visuo-haptic delayed matching task. The results indicate that cells in early stages of cortical somatosensory processing participate in haptic short-term memory.     

"The role of ventral and orbital prefrontal cortex in conditional visuomotor learning and strategy use in rhesus monkeys (Macaca mulatto)": Correction to Bussey et al (2001).

Reports an error in "The role of ventral and orbital prefrontal cortex in conditional visuomotor learning and strategy use in rhesus monkeys (Macaca mulatta)." by Timothy J. Bussey, Steven P. Wise and Elisabeth A. Murray (Behavioral Neuroscience, 2001[Oct], Vol 115[5], 971-982). In Figure 1 (p. 974), the extent of the intended lesions in the sections 32 and 28 mm from the interaural plane was misprinted. The correctly printed figure is shown in the erratum. (The following abstract of the original article appeared in record 2001-18882-001.) Four rhesus monkeys (Macaca mulatta) were trained to learn novel sets of visuomotor associations in 50 trials or less, within single test sessions. After bilateral ablation of the orbital and ventral prefrontal cortex, the monkeys lost the ability to learn these associations within a session, although they could learn them when given several daily sessions. Thus, relatively slow, across-session visuomotor learning depends on neither the ventral nor orbital prefrontal cortex, but rapid, within-session learning does. The ablations also eliminated at least 2 response strategies, repeat-stay and lose-shift, which might account, in part, for the deficit in rapid learning. The deficit is unlikely to result from a failure of visual discriminative ability or working memory: The monkeys could discriminate similar stimulus material within a session, and reducing the working memory load did not improve within-session learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perirhinal cortex and place–object conditional learning in the rat.

The present study examined whether excitotoxic lesions of the perirhinal cortex can affect acquisition of a place–object conditional task in which object and spatial information must be integrated. Testing was carried-out in a double Y-maze apparatus, in which rats learned a conditional rule of the type, "In Place X, choose Object A, not Object B (A+ vs B–); in Place Y, choose Object B, not Object A (A– vs B+)." Perirhinal cortex lesions significantly impaired acquisition of this task while sparing performance of an allocentric spatial memory task performed in a radial arm maze. Perirhinal cortex lesions also had no apparent effect on a 1-pair object discrimination task performed in the double Y-maze or on retention and acquisition of 4-pair concurrent discrimination problems performed in a computer-automated touch screen testing apparatus. The results suggest that, although the perirhinal cortex and hippocampus can be functionally dissociated, their normal mode of operation includes the integration of object and spatial information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visuospatial versus visuomotor activity in the premotor and prefrontal cortex of a primate

When visuospatial stimuli instruct a limb movement, the stimulus can be said to have both sensory and sensorimotor aspects. We studied the premotor and prefrontal areas of a rhesus monkey in order to identify neuronal activity related to the motor (or instructional) aspects of such stimuli. A rhesus monkey chose limb-movement targets according to one of two rules: (1) visuospatial stimuli instructed and triggered a limb movement toward their locations or (2) identical stimuli triggered a movement toward a predetermined target regardless of their location. Gaze and head fixation assured that each stimulus appeared at a constant location in both retinocentric and craniocentric coordinates, as well as in allocentric space. The task required that the spatial location cued by certain stimuli had to be either remembered or attended after stimulus presentation and before movement. Thus, the visuospatial information presented under one rule differed from that presented under the other only in its motor (instructional) significance and not in its attentional, spatial, mnemonic, or strictly sensory aspects. We could thereby test and confirm the hypothesis that the motor significance of visuospatial cues should commonly affect neuronal activity in the premotor cortex, but less commonly do so in the prefrontal cortex.     

Effects of dorsal noradrenergic bundle lesions on recovery after sensorimotor cortex injury

Several lines of evidence suggest that the recovery of the ability of rats to traverse a narrow beam after unilateral injury to the sensorimotor cortex is noradrenergically mediated. We tested the hypotheses that the influence of norepinephrine on beam-walking recovery occurs, at least partially, through effects in the contralateral and/or ipsilateral cerebral cortex. Rats had either a selective left or right 6-hydroxydopamine lesion or sham lesion of the dorsal noradrenergic bundle (DNB) 2 weeks before suction-ablation or sham injury of the right sensorimotor cortex. The rats' abilities to perform the beam-walking task were measured over the 10 days following cortex surgery. DNB lesions did not affect the initial severity of the beam-walking deficit and had no effect on the performance of the task in rats with sham cortex injuries. Lesions of the contralateral but not ipsilateral DNB significantly impaired recovery. Further, in cortically lesioned rats with contralateral DNB lesions, norepinephrine content in the cerebral cortex opposite to the sensorimotor cortex lesion was significantly correlated with recovery. These data suggest that the effect of norepinephrine on recovery of beam-walking ability may be partially exerted in the cerebral cortex contralateral to the injury.     

Involvement of retrosplenial cortex in forming associations between multiple sensory stimuli.

The retrosplenial cortex (RSP) is highly interconnected with medial temporal lobe structures, yet relatively little is known about its specific contributions to learning and memory. One possibility is that RSP is involved in forming associations between multiple sensory stimuli. Indeed, damage to RSP disrupts learning about spatial or contextual cues and also impairs learning about co-occurring conditioned stimuli (CSs). Two experiments were conducted to test this notion more rigorously. In Experiment 1, rats were trained in a serial feature negative discrimination task consisting of reinforced presentations of a tone alone and nonreinforced serial presentations of a light followed by the tone. Thus, in contrast to prior studies, this paradigm involved serial presentation of conditioned stimuli (CS), rather than simultaneous presentation. Rats with damage to RSP failed to acquire the discrimination, indicating that RSP is required for forming associations between sensory stimuli regardless of whether they occur serially or simultaneously. In Experiment 2, a sensory preconditioning task was used to determine if RSP was necessary for forming associations between stimuli even in the absence of reinforcement. During the first phase of this procedure, one auditory stimulus was paired with a light while a second auditory stimulus was presented alone. In the next phase of training, the same light was paired with food. During the final phase of the procedure both auditory stimuli were presented alone during a single session. Control, but not RSP-lesioned rats, exhibited more food cup behavior following presentation of the auditory cue that was previously paired with light compared with the unpaired auditory stimulus, indicating that a stimulus-stimulus association was formed during the first phase of training. These results support the idea that RSP has a fundamental role in forming associations between environmental stimuli. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Comparison of perirhinal cortex ablation and crossed unilateral lesions of the medial forebrain bundle from the inferior temporal cortex in the rhesus monkey: Effects on learning and retrieval.

Seven monkeys learned new object-reward associations and scene problems and were overtrained on 100 problems of each type. Four monkeys received crossed lesions of the medial forebrain bundle (MFB) and inferior temporal cortex, with the later addition of a fornix section ipsilateral to the MFB lesion. The remaining 3 monkeys received bilateral perirhinal cortex ablation. Disconnection of the MFB from the inferior temporal cortex impaired postoperative new learning, but the retrieval of problems overtrained preoperatively was relatively preserved. Subjects with perirhinal cortex ablation were severely impaired in new learning and at the retrieval of scene problems, but retention of object-reward associations was relatively well preserved. The results support the hypothesis that isolation of the inferior temporal cortex from basal forebrain and midbrain afferents results in dense anterograde amnesia, whereas the role of the perirhinal cortex in learning is dependent on the perceptual difficulty of the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Object and place memory in the macaque entorhinal cortex

Lesions of the entorhinal cortex in humans, monkeys, and rats impair memory for a variety of kinds of information, including memory for objects and places. To begin to understand the contribution of entorhinal cells to different forms of memory, responses of entorhinal cells were recorded as monkeys performed either an object or place memory task. The object memory task was a variation of delayed matching to sample. A sample picture was presented at the start of the trial, followed by a variable sequence of zero to four test pictures, ending with a repetition of the sample (i.e., a match). The place memory task was a variation of delayed matching to place. In this task, a cue stimulus was presented at a variable sequence of one to four "places" on a computer screen, ending with a repetition of one of the previously shown places (i.e., a match). For both tasks, the animals were rewarded for releasing a bar to the match. To solve these tasks, the monkey must 1) discriminate the stimuli, 2) maintain a memory of the appropriate stimuli during the course of the trial, and 3) evaluate whether a test stimulus matches previously presented stimuli. The responses of entorhinal cortex neurons were consistent with a role in all three of these processes in both tasks. We found that 47% and 55% of the visually responsive entorhinal cells responded selectively to the different objects or places presented during the object or place task, respectively. Similar to previous findings in prefrontal but not perirhinal cortex on the object task, some entorhinal cells had sample-specific delay activity that was maintained throughout all of the delay intervals in the sequence. For the place task, some cells had location-specific maintained activity in the delay immediately following a specific cue location. In addition, 59% and 22% of the visually responsive cells recorded during the object and place task, respectively, responded differently to the test stimuli according to whether they were matching or non-matching to the stimuli held in memory. Responses of some cells were enhanced to matching stimuli, whereas others were suppressed. This suppression or enhancement typically occurred well before the animals' behavioral response, suggesting that this information could be used to perform the task. These results indicate that entorhinal cells receive sensory information about both objects and spatial locations and that their activity carries information about objects and locations held in short-term memory.     

Video-task assessment of stimulus novelty effects on hemispheric lateralization in baboons (Papio papio).

In a video matching-to-sample task, we examined the effects of stimulus novelty on hemispheric specialization in 6 baboons (Papio papio). After familiarization with a set of 8 composite stimuli, baboons were tested with either familiar stimuli paired in a novel way, novel stimuli composed of familiar elements, or novel stimuli differing in structure from the previous stimuli. Analyses focused on visual field differences between initial and later trials in each condition. The findings reflected shorter left than right visual half-field response times for initial but not for terminal trials. With regard to accuracy, scores were smaller for the initial trials than for the later ones, but there was no significant difference between left and right visual half-fields. Overall, this study suggests that hemispheric lateralization changes with practice and that the right hemisphere of the baboon plays a critical role in the processing of novelty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Familiarity effects in visual comparison tasks and their implications for studying human intelligence.

Two experiments were carried out to study the effect of prior knowledge on cognitive processes related to human intelligence by examining its role in defining task novelty. In Exp 1, Ss performed a letter-matching task involving same–different judgments based on 4 rules of sameness; physical identity, form, system, and name. When the stimuli were unfamiliar, performance on the name classification task was correlated with measures of fluid abilities, whereas when the stimuli were familiar, performance on this task was not correlated with measures of fluid abilities. In Exp 2, Ss performed 3 different forms of a mental rotation task. When the stimuli were unfamiliar, the slope of the rotation function was correlated with a test of fluid ability, whereas when the stimuli were familiar, the slope of the rotation function was not correlated with a test of fluid ability. These results are discussed in terms of their implications for understanding the nature of task complexity and the way knowledge and processing interact in the development of skilled performance. (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.     

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.     

"Acquisition of a complex place task in rats with selective ibotenate lesions of hippocampal formation: Combined lesions of subiculum and entorthinal cortex versus hippocampus": Correction.

Reports an error in "Acquisition of a complex place task in rats with selective ibotenate lesions of hippocampal formation: Combined lesions of subiculum and entorhinal cortex versus hippocampus" by John-Paul Bouffard and Leonard E. Jarrard (Behavioral Neuroscience, 1988[Dec], Vol 102[6], 828-834). This article's corresponding plate appears on page 995. The information should read, "Plate A. Photomicrographs of horizontal, cresyl violet stained sections at dorsal, middle, and ventral levels of the brain for an unoperated control rat (left), an animal from the Subiculum + Entorhinal lesion group (middle), and a rat from the hippocampus group (right)." (The following abstract of the original article appeared in record 1989-28756-001.) The effects of isolating the hippocampus from its neocortical inputs and outputs by damaging the deep layers of entorhinal cortex and subiculum were compared with direct removal of the hippocampus using acquisition of a complex radial maze task. A series of eight problems (four out of eight arms being correct) were learned under either massed (45 s) or distributed (10 min) practice conditions, thus varying contextual information. Performance of rats with subiculum/entorhinal cortex lesions was similar to that of controls in all aspects of the radial maze task; whereas animals with hippocampal lesions were impaired on nearly all dependent measures. Although the effects of varying the intertrial interval were generally small, distributed practice did serve to facilitate the performance of hippocampal rats in terms of working memory. These findings are discussed as they related to recent theorizing in the area. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visuomotor functions of the lateral pre-motor cortex

Recent studies have provided new insights into the visuomotor functions of the dorsal and ventral regions of the lateral pre-motor cortex. Anatomical and physiological investigations in non-human primates have demonstrated that these regions have differing patterns of cortical connectivity and distinctive neuronal responses. Brain-imaging techniques and lesion studies have begun to probe the functions of homologous regions in humans.     

Saccadic eye movement and working memory deficits following damage to human prefrontal cortex

A patient with a lesion confined largely to the right inferior frontal gyrus was found to be impaired on tests of spatial working memory and executive functioning. By contrast, his pattern recognition was good. The patient's selective impairments are consistent with the view that prefrontal cortex contributes to processes involved in spatial working memory. The patient was also tested on a range of oculomotor paradigms, some of which required the temporary suppression of a saccadic response. He was unable to suppress making contra- or ipsilesional reflexive glances to peripheral stimuli on the "anti-saccade" paradigm, but his performance improved on delayed saccade, memory-guided saccade and fixation tasks. Although reflexive glances were observed under these conditions they occurred more frequently in response to contralesional stimuli than ipsilesional ones. Furthermore, the patient had no difficulty in performing anti-point movements with his ipsilesional hand. Thus, his inability to suppress reflexive glances on the anti-saccade task is not due to a generalised problem of "distractibility". The patient's deficits are discussed in terms of models of anti-saccade generation and are related to recent findings regarding the role of prefrontal cortex in working memory and visual attention.     

Premotor cortex in the rat.

J. P. Donoghue and S. P. Wise (1982) identified an area AGm in the rat that they take to be a nonprimary motor area. In the present experiments, therefore, this area was removed bilaterally in rats. The animals were poor at relearning a visual conditional motor task but were able to learn spatial delayed alternation as rapidly as unoperated animals. Thus removing this area in rats has a similar effect to removing premotor cortex in monkeys. It is argued that this dorsomedial shoulder area should not be regarded as part of prefrontal cortex in the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)