Perception and recognition memory in monkeys following lesions of area TE and perirhinal cortex.

Monkeys with lesions of perirhinal cortex (PR group) and monkeys with lesions of inferotemporal cortical area TE (TE group) were tested on a modified version of the delayed nonmatching to sample (DNMS) task that included very short delay intervals (0.5 sec) as well as longer delay intervals (1 min and 10 min). Lesions of the perirhinal cortex and lesions of area TE produced different patterns of impairment. The PR group learned the DNMS task as quickly as normal monkeys (N) when the delay between sample and choice was very short (0.5 sec). However, performance of the PR group, unlike that of the N group, fell to chance levels when the delay between sample and choice was lengthened to 10 min. In contrast to the PR group, the TE group was markedly impaired on the DNMS task even at the 0.5-sec delay, and three of four monkeys with TE lesions failed to acquire the task. The results provide support for the idea that perirhinal cortex is important not for perceptual processing, but for the formation and maintenance of long-term memory. Area TE is important for the perceptual processing of visual stimuli.

Profound amnesia after damage to the medial temporal lobe: A neuroanatomical and neuropsychological profile of patient E. P.

E. P. became profoundly amnesic in 1992 after viral encephalitis, which damaged his medial temporal lobe bilaterally. Because of the rarity of such patients, we have performed a detailed neuroanatomical analysis of E. P.'s lesion using magnetic resonance imaging, and we have assessed his cognitive abilities with a wide range of neuropsychological tests. Finally, we have compared and contrasted the findings for E. P. with the noted amnesic patient H.M, whose surgical lesion is strikingly similar to E. P.'s lesion.

Impaired recognition memory in monkeys after damage limited to the hippocampal region.

Monkeys with lesions limited to the hippocampal region (the hippocampus proper, the dentate gyrus, and the subiculum) were impaired on two tasks of recognition memory: delayed nonmatching to sample and the visual paired-comparison task. Recognition memory was impaired in five different groups of monkeys, whether the lesions were made by an ischemic procedure, by radio frequency, or by ibotenic acid. The finding that the hippocampal region is essential for normal recognition memory performance is considered in the context of current ideas about the role of the hippocampus in declarative memory.

Memory distortions develop over time: recollections of the O.J. Simpson trial verdict after 15 and 32 months.

Fifteen or 32 months after the verdict was announced in the O.J. Simpson murder trial, we asked college students about how they had heard the news, and we compared their responses with what they had told us 3 days after the verdict. Our study is the first to have assessed recollective accuracy at two different intervals more than 1 year after a noted public event. The quality of the recollections after 32 months was strikingly different from the quality of the recollections after 15 months. After 15 months, 50% of the recollections were highly accurate, and only 11% contained major errors or distortions. After 32 months, only 29% of the recollections were highly accurate, and more than 40% contained major distortions. Retention interval appears to be an important factor determining the frequency of memory distortions, and differences in the retention interval across studies may account for some of the contradictions in the flashbulb-memory literature. Metamemory errors and source memory difficulties are a likely basis of poor memory performance after long retention intervals. The results highlight the marked qualitative changes in recollections that can occur between 1 and 3 years after information has been acquired.

Operant test battery performance in children: correlation with IQ.

The relationship between intelligence and money-(nickel-)reinforced operant behaviors were compared in 115 six year old children. The Operant Test Battery (OTB) consists of tasks thought to engender responses dependent upon specific brain functions that include motivation, color and position discrimination, learning, short-term memory, and time estimation. OTB endpoints were compared with Full Scale, Verbal and Performance IQ scores. Highly significant correlations were noted between several OTB measures (e.g., color and position discrimination accuracy) and IQ scores, but not in others (e.g., motivation task response rate). The results demonstrate the relevance of these measures as metrics of important brain functions. Additionally, since laboratory animals can readily perform these same tasks, these kinds of behaviors in laboratory animals should be useful in studying the effects of neuroactive/neurotoxic compounds on aspects of cognitive function in animals and in predicting adverse effects of such agents on related brain functions in humans.

Dissociation between the effects of damage to perirhinal cortex and area TE.

Perirhinal cortex and area TE are immediately adjacent to each other in the temporal lobe and reciprocally interconnected. These areas are thought to lie at the interface between visual perception and visual memory, but it has been unclear what their separate contributions might be. In three experiments, monkeys with bilateral lesions of the perirhinal cortex exhibited a different pattern of impairment than monkeys with bilateral lesions of area TE. In experiment 1, lesions of the perirhinal cortex produced a multimodal deficit in recognition memory (delayed nonmatching to sample), whereas lesions of area TE impaired performance only in the visual modality. In experiment 2, on a test of visual recognition memory (the visual paired comparison task) lesions of the perirhinal cortex impaired performance at long delays but spared performance at a very short delay. In contrast, lesions of area TE impaired performance even at the short delay. In experiment 3, lesions of the perirhinal cortex and lesions of area TE produced an opposite pattern of impairment on two visual discrimination tasks, simple object discrimination learning (impaired only by perirhinal lesions), and concurrent discrimination learning (impaired only by TE lesions). Taken together, the findings suggest that the perirhinal cortex, like other medial temporal lobe structures, is important for the formation of memory, whereas area TE is important for visual perceptual processing.

The human perirhinal cortex and recognition memory.

The importance of the perirhinal cortex for visual recognition memory performance is undisputed. However, it has not been clear whether its contribution to performance is mainly perceptual, or mainly mnemonic, or whether the perirhinal cortex contributes to both perception and memory. We determined the effects of medial temporal lobe damage that includes complete damage to the perirhinal cortex in two amnesic patients by assessing recognition memory for complex visual stimuli across delays from 0 to 40 s. These patients, as well as six other amnesic patients with damage limited to the hippocampal formation or diencephalic structures, exhibited intact recognition memory at delays of 0-2 s and a delay-dependent memory impairment at delays of 6 s and longer. Additionally, the patients with damage to the perirhinal cortex performed worse than the other amnesic patients at delays of 25 s and longer. The findings suggest that the perirhinal cortex is not important for visual perception or immediate memory. In this respect, the findings for perirhinal cortex resemble the findings for other medial temporal lobe structures, including the hippocampus.

A reexamination of the concurrent discrimination learning task: the importance of anterior inferotemporal cortex, area TE.

For 30 years, the concurrent discrimination learning task has figured prominently in studies used to determine the effects of medial temporal lobe damage in monkeys. However, the findings from these studies have been contradictory. We explored the contribution to concurrent discrimination performance of inadvertent damage to area TE by reexamining the behavioral data and histological material from monkeys with medial temporal lobe lesions previously tested in our laboratory. The amount of inadvertent damage to area TE was more predictive of impaired performance on the concurrent discrimination learning task than was the amount of damage to any medial temporal lobe structure, including the perirhinal cortex. These findings resolve earlier inconsistent findings regarding the concurrent discrimination learning task by demonstrating that performance on this task depends on area TE and not on perirhinal cortex or other medial temporal lobe structures.

Acute behavioral effects of MK-801 in rhesus monkeys: assessment using an operant test battery.

The acute effects of MK-801, a selective, noncompetitive NMDA receptor antagonist, were assessed using an operant test battery (OTB) of complex food-reinforced tasks that are thought to depend upon relatively specific brain functions such as motivation to work for food (progressive ratio, PR), learning (incremental repeated acquisition, IRA), color and position discrimination (conditioned position responding, CPR), time estimation (temporal response differentiation, TRD), and short-term memory and attention (delayed matching-to-sample, DMTS). Endpoints included response rates (RR), accuracies (ACC), and percent task completed (PTC). MK-801 (0.003-0.075 mg/kg, IV), given 15 min pretesting, produced significant dose-dependent decreases in measures of IRA and TRD performance at doses > or = 0.03 mg/kg. In both tasks, MK-801 produced significant decreases in accuracy at doses lower than those required to affect response rate. MK-801 also produced statistically significant decreases in PR, CPR, and DMTS measures, but only at higher doses (> or = 0.056 mg/kg) that caused significant decreases in both response rates and accuracies. These results indicate that, in monkeys, performance of operant tasks designed to model learning and time estimation is more sensitive to the disruptive effects of MK-801 than performance of tasks that model motivation, color, and position discrimination, and short-term memory and attention.

Acute effects of caffeine on several operant behaviors in rhesus monkeys.

The acute effects of 1,3-trimethylxanthine (caffeine) were assessed using an operant test battery (OTB) of complex food-reinforced tasks that are thought to depend upon relatively specific brain functions, such as motivation to work for food (progressive ratio, PR), learning (incremental repeated acquisition, IRA), color and position discrimination (conditioned position responding, CPR), time estimation (temporal response differentiation, TRD), and short-term memory and attention (delayed matching-to-sample, DMTS). Endpoints included response rates (RR), accuracies (ACC), and percent task completed (PTC). Caffeine sulfate (0.175-20.0 mg/kg, IV), given 15 min pretesting, produced significant dose-dependent decreases in TRD percent task completed and accuracy at doses > or = 5.6 mg/kg. Caffeine produced no systematic effects on either DMTS or PR responding, but low doses tended to enhance performance in both IRA and CPR tasks. Thus, in monkeys, performance of an operant task designed to model time estimation is more sensitive to the disruptive effects of caffeine than is performance of the other tasks in the OTB.