RESUMEN

Two patients with large lesions of the medial temporal lobe were given four tests of semantic knowledge that could only have been acquired after the onset of their amnesia. In contrast to previous studies of postmorbid semantic learning, correct answers could be based on a simple, nonspecific sense of familiarity about single words, faces, or objects. According to recent computational models (for example, Norman and O'Reilly (2003) Psychol Rev 110:611-646), this characteristic should be optimal for detecting the kind of semantic learning that might be supported directly by the neocortex. Both patients exhibited some capacity for new learning, albeit at a level substantially below control performances. Notably, the correct answers appeared to reflect declarative memory. It was not the case that the correct answers simply popped out in some automatic way in the absence of any additional knowledge about the items. Rather, the few correct choices made by the patients tended to be accompanied by additional information about the chosen items, and the available knowledge appeared to be similar qualitatively to the kind of factual knowledge that healthy individuals gradually acquire over the years. The results are consistent with the idea that neocortical structures outside the medial temporal lobe are able to support some semantic learning, albeit to a very limited extent. Alternatively, the small amount of learning detected in the present study could depend on tissue within the posterior medial temporal lobe that remains intact in both patients.

Asunto(s)

Discapacidades para el Aprendizaje/fisiopatología , Trastornos de la Memoria/fisiopatología , Lóbulo Temporal/fisiopatología , Anciano de 80 o más Años , Amnesia Anterógrada/etiología , Amnesia Anterógrada/patología , Amnesia Anterógrada/fisiopatología , Encefalitis Viral/complicaciones , Encefalitis Viral/patología , Corteza Entorrinal/patología , Corteza Entorrinal/fisiopatología , Cara , Hipocampo/patología , Hipocampo/fisiopatología , Artículos Domésticos , Humanos , Pruebas del Lenguaje , Discapacidades para el Aprendizaje/etiología , Discapacidades para el Aprendizaje/patología , Masculino , Trastornos de la Memoria/etiología , Trastornos de la Memoria/patología , Recuerdo Mental , Persona de Mediana Edad , Reconocimiento Visual de Modelos , Prosopagnosia/etiología , Prosopagnosia/patología , Prosopagnosia/fisiopatología , Reconocimiento en Psicología , Lóbulo Temporal/patología

RESUMEN

Two recent studies reported that yes/no recognition can be more impaired by hippocampal lesions than forced-choice recognition when the targets and foils are highly similar. This finding has been taken in support of two fundamental proposals: (1) yes/no recognition tests depend more on recollection than do forced-choice tests; and (2) the hippocampus selectively supports the recollection process. Using the same stimulus materials as in the earlier studies, we tested five memory-impaired patients with circumscribed hippocampal lesions and 15 controls. As in the earlier studies, participants studied 12 pictures of objects and then took either a 12-item forced-choice test with four alternatives or a 60-item yes/no test. Patients were impaired on both tests but did more poorly on the yes/no test. However, a yes/no test based on 12 study items would conventionally involve only 24 test items (i.e., 12 study items and 12 foil items). When we scored only the first 24 test items, the patients performed identically on the yes/no and forced-choice tests. Examination of the data in blocks of 12 trials indicated that the scores of the patients declined as testing continued. We suggest that a yes/no test of 60 items is difficult relative to a 12-item forced-choice test due to the increased study-test delay and due to increased interference, not because of any fundamental difference between the yes/no and forced-choice formats. We conclude that hippocampal lesions impair yes/no and forced-choice recognition to the same extent.

Asunto(s)

Toma de Decisiones/fisiología , Hipocampo/fisiopatología , Reconocimiento en Psicología/fisiología , Adulto , Anciano , Discriminación en Psicología , Femenino , Humanos , Masculino , Trastornos de la Memoria/patología , Persona de Mediana Edad , Pruebas Neuropsicológicas

RESUMEN

Repetition priming has been shown to be independent of recognition memory. Thus, the severely amnesic patient E.P. has demonstrated intact stem completion priming and perceptual identification priming, despite at-chance performance on recognition memory tasks. It has also been shown that perceptual fluency can influence feelings of familiarity, in the sense that items perceived more quickly tend to be identified as familiar. If studied items are identified more fluently, due to perceptual priming, and fluency leads to familiarity, why do severely amnesic patients perform no better than chance on recognition memory tasks? One possibility is that severely amnesic patients do not exhibit normal fluency. Another possibility is that fluency is not a sufficiently strong cue for familiarity. In two experiments, 2 severely amnesic patients, 3 moderately amnesic patients, and 8 controls saw words slowly clearing from a mask. The participants identified each word as quickly as possible and then made a recognition (old/new) judgment. All the participants exhibited fluency, in that old responses were associated with shorter identification times than new responses were. In addition, for the severely amnesic patients, priming was intact, and recognition memory performance was at chance. We next calculated how much priming and fluency should elevate the probability of accurate recognition. The tendency to identify studied words rapidly (.6) and the tendency to label these rapidly identified words old (.6) would result in 36% of the studied words being labeled old. Other studied words were identified slowly (.4) but were still labeled old (.4), resulting in an additional 16% of studied words labeled old. Thus, the presence of fluency increases the probability of accurate recognition judgments to only 52% (chance = 50%). This finding explains why amnesic patients can exhibit both priming and fluency yet still perform at chance on recognition tests.

Asunto(s)

Amnesia/fisiopatología , Amnesia/psicología , Aprendizaje por Asociación de Pares/fisiología , Percepción/fisiología , Reconocimiento en Psicología/fisiología , Adulto , Anciano , Anciano de 80 o más Años , Estudios de Casos y Controles , Hipocampo/fisiopatología , Humanos , Masculino , Pruebas Neuropsicológicas/estadística & datos numéricos , Enmascaramiento Perceptual , Tiempo de Reacción/fisiología , Estudios Retrospectivos , Lóbulo Temporal/fisiopatología

RESUMEN

Priming is an unconscious (nondeclarative) form of memory whereby identification or production of an item is improved by an earlier encounter. It has been proposed that declarative memory and priming might be related-for example, that conceptual priming results in more fluent processing, thereby providing a basis for familiarity judgments. In two experiments, we assessed conceptual priming and recognition memory across a 5-min interval in 5 memory-impaired patients. All patients exhibited fully intact priming in tests of both free association (study tent; at test, provide an association to canvas) and category verification (study lemon; at test, decide: Is lemon a type of fruit?). Yet the 2 most severely amnesic patients performed at chance on matched tests of recognition memory. These findings count against the notion that conceptual priming provides feelings of familiarity that can support accurate recognition judgments. We suggest that priming is inaccessible to conscious awareness and does not influence declarative memory.

Asunto(s)

Cognición , Memoria , Pruebas de Asociación de Palabras , Femenino , Humanos , Juicio , Masculino , Escalas de Wechsler

RESUMEN

Semantic knowledge (e.g., long-established knowledge about objects, facts, and word meanings) is known to be severely impaired by damage to the anterolateral temporal lobe. For example, patients with semantic dementia have prominent atrophy in anterolateral temporal cortex and also have significant damage within the medial aspect of the temporal lobe. However, there is uncertainty about the contribution of medial temporal lobe damage, including perirhinal cortex damage, to impaired semantic knowledge. Drawing largely on published material from multiple sources, we compared the performance of severely amnesic patients with large medial temporal lobe lesions and patients with semantic dementia on nine tests of semantic knowledge and two tests of new learning ability. On the tests of semantic knowledge, the amnesic patients performed markedly better than the patients with semantic dementia. By contrast, on the tests of new learning, the patients with semantic dementia performed markedly better than the amnesic patients. We conclude that medial temporal lobe damage impairs the formation of declarative memory, and that semantic knowledge is impaired to the extent that damage extends laterally in the temporal lobe. Reports that the extent of atrophy in perirhinal cortex correlated with the severity of impaired semantic knowledge may be understood by supposing that the extent of damage in many temporal lobe areas is intercorrelated in this progressive disease, and that the extent of atrophy in perirhinal cortex is a proxy for the overall severity of dementia.

Asunto(s)

Conocimiento , Semántica , Lóbulo Temporal/anatomía & histología , Anciano , Humanos , Imagen por Resonancia Magnética , Masculino

RESUMEN

By using blocked and rapid event-related functional MRI studies of memory, we explored the implications of using rest periods as a baseline condition in functional MRI studies. Activity in the medial temporal lobe (as well as in other brain regions) was substantially higher during rest than during several alternative baseline conditions. The effect of this elevated activity during rest was to reduce, eliminate, or even reverse the sign of the activity during task conditions relevant to memory functions. The results demonstrate that periods of rest are associated with significant cognitive activity and, therefore, provide a nonoptimal baseline for memory tasks. These results were observed not only when relatively long blocks of rest were used (experiment 1), but also when rest consisted of the short null trials typically used in rapid event-related designs (experiment 2). The findings have important implications for the design and interpretation of a wide range of fMRI studies of cognition.

Asunto(s)

Cognición , Imagen por Resonancia Magnética , Adulto , Corteza Cerebral/fisiología , Femenino , Hipocampo/fisiología , Humanos , Masculino

RESUMEN

Two tests of auditory recognition memory were given to four patients with bilateral hippocampal damage (H+) and three patients with large medial temporal lobe lesions and additional variable damage to lateral temporal cortex (MTL+). When single stimuli were presented, performance was normal across delays as long as 30 sec, presumably because information could be maintained in working memory through rehearsal. When lists of 10 stimuli were presented, performance was impaired after a 5-min delay. Patients with MTL+ lesions performed marginally worse than patients with H+ lesions, consistent with findings for recognition memory in other modalities. The findings show that auditory recognition, like recognition memory in other sensory modalities, is dependent on the medial temporal lobe.

Asunto(s)

Amnesia/psicología , Percepción Auditiva/fisiología , Memoria/fisiología , Lóbulo Temporal/lesiones , Estimulación Acústica , Anciano , Femenino , Hipocampo/fisiología , Humanos , Masculino , Persona de Mediana Edad

RESUMEN

Visual stimuli that are frequently seen together become associated in long-term memory, such that the sight of one stimulus readily brings to mind the thought or image of the other. It has been hypothesized that acquisition of such long-term associative memories proceeds via the strengthening of connections between neurons representing the associated stimuli, such that a neuron initially responding only to one stimulus of an associated pair eventually comes to respond to both. Consistent with this hypothesis, studies have demonstrated that individual neurons in the primate inferior temporal cortex tend to exhibit similar responses to pairs of visual stimuli that have become behaviorally associated. In the present study, we investigated the role of these areas in the formation of conditional visual associations by monitoring the responses of individual neurons during the learning of new stimulus pairs. We found that many neurons in both area TE and perirhinal cortex came to elicit more similar neuronal responses to paired stimuli as learning proceeded. Moreover, these neuronal response changes were learning-dependent and proceeded with an average time course that paralleled learning. This experience-dependent plasticity of sensory representations in the cerebral cortex may underlie the learning of associations between objects.

Asunto(s)

Aprendizaje/fisiología , Neuronas/fisiología , Lóbulo Temporal/fisiología , Animales , Macaca mulatta , Masculino , Estimulación Luminosa , Análisis y Desempeño de Tareas , Lóbulo Temporal/citología

RESUMEN

Although it is well established that the hippocampal region is involved in the formation of declarative memory, the exact nature of its involvement is unclear. One view is that the hippocampal region is involved only in tasks that require the formation or use of associations. According to this view, the hippocampal region is not involved in traditional tests of recognition memory. An alternative view is that the hippocampal region combines and extends the processing carried out by structures in the parahippocampal gyrus and that it is involved in all forms of declarative memory, including recognition memory. Using event-related functional magnetic resonance imaging (fMRI), we observed hippocampal activity during both traditional and associative recognition memory tasks. Critically, the hippocampal region was no more active in the associative recognition task than in the traditional recognition task.

Asunto(s)

Aprendizaje por Asociación/fisiología , Hipocampo/fisiología , Reconocimiento en Psicología/fisiología , Adulto , Femenino , Humanos , Imagen por Resonancia Magnética , Masculino , Giro Parahipocampal/fisiología

RESUMEN

We tested the proposal that trace and delay eyeblink conditioning aref fundamentally different kinds of learning. Strings of one, two, three, or four trials with the conditioned stimulus (CS) alone and strings of one, two, three, or four trials with paired presentations of both the CS and the unconditioned stimulus (US) occurred in such a way that the probability of a US was independent of string length. Before each trial, participants predicted the likelihood of the US on the next trial. During both delay (n = 20) and trace (n = 18) conditioning, participants exhibited high expectation of the US following strings of CS-alone trials and low expectation of the US following strings of CS-US trials--a phenomenon known as the gambler's fallacy. During delay conditioning, conditioned responses (CRs) were not influenced by expectancy but by the associative strength of the CS and US. Thus, CR probability was high following a string of CS-US trials and low following a string of CS-alone trials. The results for trace conditioning were opposite. CR probability was high when expectancy of the US was high and low when expectancy of the US was low: The results show that trace and delay eyeblink conditioning are fundamentally different phenomena. We consider how the findings can be understood in terms of the declarative and nondeclarative memory systems that support eyeblink classical conditioning.

Asunto(s)

Parpadeo/fisiología , Condicionamiento Psicológico , Memoria/fisiología , Adolescente , Adulto , Femenino , Humanos , Masculino

RESUMEN

Rats with ibotenic acid lesions of the hippocampus (H-IBO) were trained on the trial-unique delayed nonmatching-to-sample task (DNMS) using a short delay of 4 s. The H-IBO group learned the nonmatching rule as quickly as control animals. However, performance was impaired on the DNMS task when the delay between the sample and choice phase was increased to 1 or 2 min. The use of 4-s delay (probe) trials indicated that the H-IBO animals retained the nonmatching-to-sample rule throughout testing. In a second experiment, using the same groups of rats, extended training at the 1-min delay did not ameliorate the deficit produced by H-IBO lesions. The finding of impaired recognition memory in rats after hippocampal lesions is consistent with findings from humans and monkeys. Several methodological issues are considered that have complicated the interpretation of earlier studies of recognition memory in rats following hippocampal lesions. The capacity for recognition memory in humans, monkeys, and rodents is discussed as a straightforward example of hippocampus-dependent (declarative) memory.

Asunto(s)

Hipocampo/fisiología , Memoria/fisiología , Animales , Conducta Animal/fisiología , Aprendizaje Discriminativo/fisiología , Agonistas de Aminoácidos Excitadores/farmacología , Hipocampo/efectos de los fármacos , Hipocampo/patología , Ácido Iboténico/farmacología , Masculino , Pruebas Neuropsicológicas , Ratas , Ratas Long-Evans , Valores de Referencia , Factores de Tiempo

RESUMEN

Two recent meta-analyses, drawing on data from many of the same studies with monkeys, reached different conclusions about the relationship between hippocampal damage and recognition memory performance. Both studies found evidence of recognition memory impairment following hippocampal damage. However, Zola et al. (J Neurosci 2000;20:451-463) found no significant correlation between extent of hippocampal damage and recognition memory performance, whereas Baxter and Murray (Hippocampus 2001;11:61-71) concluded that the extent of hippocampal damage in monkeys was inversely correlated with impaired performance. Here, we first consider the requirements for carrying out a valid meta-analysis, and point out that the analysis carried out by Baxter and Murray (Hippocampus 2001;11:61-71) is invalid on simple statistical grounds. We then adopt the appropriate statistical procedures (multiple regression analyses rather than simple correlational analysis) to assess the relationship between extent of hippocampal damage and recognition performance across different studies. None of these analyses, including a reanalysis of the data of Baxter and Murray (Hippocampus 2001;11:61-71), revealed a significant inverse relationship between lesion size and behavioral impairment. Most of the variance was explained by differences between the studies that contributed to the meta-analysis, not by lesion size itself. Indeed, analysis of covariance indicated that there were differences among the studies beyond lesion size that significantly affected performance. Finally, we consider what relationship might hold between lesion size and memory performance in the monkey.

Asunto(s)

Hipocampo/patología , Memoria/fisiología , Animales , Haplorrinos , Metaanálisis como Asunto , Análisis de Regresión

RESUMEN

In humans, the phenomenon of temporally graded retrograde amnesia has been described in the clinic and the laboratory for more than 100 years. In the 1990s, retrograde amnesia began to be studied prospectively in experimental animals. We identified 13 published studies in which animals were given equivalent training at two or more separate times before damage to the fornix or hippocampal formation. Eleven of these studies found temporally graded retrograde amnesia, with the extent of amnesia ranging from several days to a month or two. We consider these studies and also suggest why temporally graded retrograde amnesia has sometimes not been observed. Although the evidence in favor of temporally graded retrograde amnesia is substantial, the inference from this work, that memory is reorganized as time passes, is rather vague and depends on mechanisms yet to be identified. It is therefore encouraging that many opportunities exist for moving beyond purely descriptive studies to studies that involve treatments or manipulations directed toward yielding information about mechanisms.

Asunto(s)

Amnesia Retrógrada/fisiopatología , Hipocampo/fisiopatología , Animales , Corteza Entorrinal/fisiopatología , Fórnix/fisiopatología , Humanos

RESUMEN

Two patients (E.P. and G.T.) were previously described with damage to amygdala and anterior temporal cortex (S.B. Hamann et al., 1996). Both rated emotions in facial expressions normally (the rating task) when the data analysis followed a method that had revealed an impairment in the well-studied patient S.M. The present study reports findings for a 3rd patient (G.P.) with the rating task and reexamines the data for E.P. and G.T. All 3 patients were also given a labeling task in which they selected, from a list of 6 words, which word they thought best described the emotion expressed by a face. All 3 patients were unmistakably impaired on both tasks. However, the impairment exhibited by these patients is different from S.M.'s impairment. The difference may depend on the etiology (congenital vs. adult-onset lesion) or the site of the damage (relatively selective amygdala damage vs. damage to amygdala as well as anterior temporal cortex).

Asunto(s)

Emociones , Expresión Facial , Percepción Social , Lóbulo Temporal/fisiopatología , Anciano , Amnesia/patología , Amnesia/psicología , Amígdala del Cerebelo/patología , Encefalitis por Herpes Simple/patología , Encefalitis por Herpes Simple/psicología , Humanos , Masculino , Persona de Mediana Edad , Lóbulo Temporal/patología

RESUMEN

Declarative memory depends on the hippocampus and related medial temporal lobe and diencephalic structures. Declarative memory has usually been found to be available to conscious recollection. A recent study (Chun and Phelps, Nat Neurosci 1999;2:844-847) found that damage to the medial temporal lobe (including the hippocampus) impaired performance on a perceptual learning task, yet the learning was accomplished in the absence of memory for the stimuli. This finding raised the possibility that some hippocampus-dependent tasks may be inaccessible to awareness and may be performed without evoking conscious memory processes. Using the same task, we show that when damage is confined largely to the hippocampal formation, perceptual learning is intact. Thus, the available data suggest that damage limited to the hippocampal formation does not impair nonconscious (nondeclarative) memory. Further, the data do not contradict the idea that hippocampus dependent memory is accessible to conscious recollection. Finally, perceptual learning was impaired in patients, with extensive damage to the medial temporal lobe and with additional variable damage to lateral temporal cortex.

Asunto(s)

Amnesia/fisiopatología , Amnesia/psicología , Concienciación/fisiología , Hipocampo/fisiopatología , Aprendizaje/fisiología , Percepción/fisiología , Anciano , Amnesia/diagnóstico , Amnesia/etiología , Encefalitis Viral/diagnóstico , Encefalitis Viral/fisiopatología , Encefalitis Viral/psicología , Femenino , Hipocampo/patología , Humanos , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Tiempo de Reacción , Valores de Referencia , Índice de Severidad de la Enfermedad , Lóbulo Temporal/patología

RESUMEN

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.

Asunto(s)

Memoria/fisiología , Reconocimiento Visual de Modelos/fisiología , Percepción/fisiología , Lóbulo Temporal/fisiología , Animales , Macaca fascicularis , Masculino , Giro Parahipocampal/patología , Giro Parahipocampal/fisiología , Lóbulo Temporal/patología

RESUMEN

Amnesic patients and controls listened to verbal descriptions of imaginary animals and then classified novel descriptions according to whether they belonged to the studied category. Controls performed well, but the amnesic patients did not acquire categorical knowledge. These findings contrast with previous demonstrations of intact category learning by amnesic patients for dot patterns, artificial grammars, and cartoon animals. It appears that category knowledge can be acquired implicitly when training exemplars are presented visually and when the similarities among items can be readily perceived. Verbal category learning requires the extraction and retention of meaning from training exemplars that are separated in time and may make demands on declarative memory that are beyond the capacity of amnesic patients.

Asunto(s)

Amnesia/fisiopatología , Aprendizaje Verbal/fisiología , Amnesia/diagnóstico , Atrofia/patología , Femenino , Lóbulo Frontal/patología , Hipocampo/patología , Humanos , Imagen por Resonancia Magnética , Masculino , Pruebas Neuropsicológicas , Índice de Severidad de la Enfermedad , Tálamo/patología

RESUMEN

Trace eyeblink conditioning (with a trace interval >/=500 msec) depends on the integrity of the hippocampus and requires that participants develop awareness of the stimulus contingencies (i.e., awareness that the conditioned stimulus [CS] predicts the unconditioned stimulus [US]). Previous investigations of the relationship between trace eyeblink conditioning and awareness of the stimulus contingencies have manipulated awareness or have assessed awareness at fixed intervals during and after the conditioning session. In this study, we tracked the development of knowledge about the stimulus contingencies trial by trial by asking participants to try to predict either the onset of the US or the onset of their eyeblinks during differential trace eyeblink conditioning. Asking participants to predict their eyeblinks inhibited both the acquisition of awareness and eyeblink conditioning. In contrast, asking participants to predict the onset of the US promoted awareness and facilitated conditioning. Acquisition of knowledge about the stimulus contingencies and acquisition of differential trace eyeblink conditioning developed approximately in parallel (i.e., concurrently).

Asunto(s)

Concienciación/fisiología , Parpadeo/fisiología , Condicionamiento Clásico/fisiología , Anciano , Aire , Femenino , Predicción , Humanos , Conocimiento , Masculino , Persona de Mediana Edad , Estimulación Física

RESUMEN

While the role of the perirhinal cortex in declarative memory has been well established, it has been unclear whether the perirhinal cortex might serve an additional nonmnemonic role in visual perception. Evidence that the perirhinal cortex might be important for visual perception comes from a recent report that monkeys with perirhinal cortical lesions are impaired on difficult (but not on simple) visual discrimination tasks. We administered these same tasks to nine amnesic patients, including three severely impaired patients with complete damage to perirhinal cortex bilaterally (E.P., G.P., and G.T.). The patients performed all tasks as well as controls. We suggest that the function of perirhinal cortex as well as antero-lateral temporal cortex may differ between humans and monkeys.

Asunto(s)

Discriminación en Psicología/fisiología , Vías Olfatorias/fisiología , Percepción Visual/fisiología , Anciano , Amnesia/diagnóstico , Amnesia/fisiopatología , Amnesia/psicología , Color , Cara , Femenino , Humanos , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Ruido , Vías Olfatorias/patología , Vías Olfatorias/fisiopatología , Reconocimiento Visual de Modelos , Enmascaramiento Perceptual , Valores de Referencia , Percepción Espacial/fisiología

RESUMEN

Performance on the visual paired-comparison task depends on the integrity of the hippocampal formation in humans, monkeys, and, for an analogous task, in rats. The present study sought additional evidence in healthy volunteers concerning the nature of this task. We found that performance on the visual paired-comparison task was predictive of subsequent recognition memory performance whereas perceptual priming was unrelated to subsequent recognition memory performance. The results are consistent with the data from lesions and suggest that performance on the visual paired-comparison task measures a form of declarative memory.

Asunto(s)

Memoria/fisiología , Visión Ocular/fisiología , Humanos