Novelty encoding networks in the human brain: positron emission tomography data

Data from positron emission tomography (PET) studies showed novelty activations--higher regional cerebral blood flow associated with perceiving novel rather than familiar stimuli. Regions in the right 'expanded' limbic system--hippocampal formation, parahippocampal gyrus, retrosplenial cortex, thalamus, subcallosal area, the border between cortical areas 32 and 10, anterior and inferior cingulate cortex, putamen, and medial prefrontal cortex--showed such activations for complex pictures. Because novel information is usually encoded for storage in memory, these regions can be seen as constituting components of a visual/spatial novelty encoding network. Insular, opercular and temporal regions (e.g. area 37) showed novelty activations not only for visual pictures but also for auditorily presented sentences, and can be thought of as components of a transmodal novelty encoding network.

The role of the left prefrontal cortex in verbal processing: semantic processing or willed action?

This study was designed to test the various proposed explanations (semantic processing, willed action, production of a spoken response) for the unilateral activation of the left prefrontal cortex noted in PET studies of verbal processing. Twenty subjects underwent 15O-water PET scans while undertaking a lexical task (detecting the letter 'a' in visually presented words) and a semantic task (categorizing nouns into living/non-living). The semantic task resulted in a significant unilateral left dorsolateral prefrontal activation. This finding suggests that the left inferior prefrontal cortex is the anatomical region involved in 'working with meaning', and that the activation does not reflect willed action, is not task-specific and is not attributable to the requirements of a spoken response.

Cognitive processes and cerebral cortical fundi: findings from positron-emission tomography studies

Positron-emission tomography (PET) studies of regional cerebral blood flow have provided evidence relevant to localization of cognitive functions. The critical loci identified in these studies are typically described in terms of macroanatomically labeled cortical and subcortical regions. We report the results of a meta-analysis of localization of changes in blood flow, based on nearly 1000 cerebral cortical peaks of activity obtained from groups of subjects in 30 PET studies. The results showed that, on average, 47% of these peaks were localized within the fundus regions of cortical sulci. This is an unexpectedly high proportion because fundal regions compose < 8% of the cortical mantle. Further analysis suggested a coarse correlation between the extent of fundal activation observed in different studies and the estimated cognitive complexity of the tasks used in the studies. These findings are potentially interesting because (i) the preponderance of fundal activation has implications for the interpretation of the PET data, (ii) they suggest that cortical sulcal and fundal regions may play a distinctive role in higher cognitive processing, or (iii) both of the above.

Reducing retroactive interference: an interference analysis

In 4 experiments on retroactive interference (RI), we varied paired-associate learning lists that produced either appreciable or negligible forgetting. When the category of the stimulus word predicted its response word category, and the response was relatively unique within its category, learning was extremely rapid, and negative transfer and RI were negligible. The more the competing primed items in the predicted response category, the slower the learning and the greater the RI. If cues and responses were unrelated, learning was very slow, and RI was appreciable. Thus, predictive relations that help stimuli retrieve unique responses greatly alter forgetting in RI paradigms.

Neuroanatomical correlates of encoding in episodic memory: levels of processing effect

Cognitive studies of memory processes demonstrate that memory for stimuli is a function of how they are encoded; stimuli processed semantically are better remembered than those processed in a perceptual or shallow fashion. This study investigates the neural correlates of this cognitive phenomenon. Twelve subjects performed two different cognitive tasks on a series of visually presented nouns. In one task, subjects detected the presence or absence of the letter a; in the other, subjects categorized each noun as living or nonliving. Positron emission tomography (PET) scans using 15O-labeled water were obtained during both tasks. Subjects showed substantially better recognition memory for nouns seen in the living/nonliving task, compared to nouns seen in the a-checking task. Comparison of the PET images between the two cognitive tasks revealed a significant activation in the left inferior prefrontal cortex (Brodmann's areas 45, 46, 47, and 10) in the semantic task as compared to the perceptual task. We propose that memory processes are subserved by a wide neurocognitive network and that encoding processes involve preferential activation of the structures in the left inferior prefrontal cortex.

Hemispheric encoding/retrieval asymmetry in episodic memory: positron emission tomography findings

Data are reviewed from positron emission tomography studies of encoding and retrieval processes in episodic memory. These data suggest a hemispheric encoding/retrieval asymmetry model of prefrontal involvement in encoding and retrieval of episodic memory. According to this model, the left and right prefrontal lobes are part of an extensive neuronal network that subserves episodic remembering, but the two prefrontal hemispheres play different roles. Left prefrontal cortical regions are differentially more involved in retrieval of information from semantic memory and in simultaneously encoding novel aspects of the retrieved information into episodic memory. Right prefrontal cortical regions, on the other hand, are differentially more involved in episodic memory retrieval.

Neuroanatomical correlates of retrieval in episodic memory: auditory sentence recognition

This study used positron emission tomography (PET) to investigate the neuroanatomical correlates of remembering previously experienced events. Twelve young healthy adults listened to "old" meaningful sentences which they had studied 24 hr previously. As a control task the subjects listened to comparable "new" sentences that they had never heard before. Regional cerebral blood flow associated with each task was measured by PET scans using 15O-labeled water. Comparison (old-sentence task minus new-sentence task) of the PET images revealed an extended strip of increased blood flow in the right dorsolateral prefrontal cortex (Brodmann's areas 10, 46, and 9) and the anterior portion of area 6. Other principal regions of increased blood flow were situated around the left anterior cingulate sulcus and bilaterally in the parietal lobes (areas 7 and 40). Major decreases in blood flow were situated bilaterally in the temporal lobes (areas 21, 22, 41, and 42). A high proportion of activity changes seemed to be located in the depths of cortical sulci. Increases in blood flow are seen as reflecting the operations of a widely distributed neuronal network involving prefrontal and parietal cortical regions that subserves the conscious recollection of previously experienced events. Decreases in blood flow in the temporal auditory areas are interpreted as reflecting auditory priming. The prevalence of sulcal blood-flow changes may reflect extensive cortical gyrification; it may also indicate that memory-related processes rely on the densely packed neuropil of sulcal regions.

Reducing retroactive interference: an interference analysis

In 4 experiments on retroactive interference (RI), we varied paired-associate learning lists that produced either appreciable or negligible forgetting. When the category of the stimulus word predicted its response word category, and the response was relatively unique within its category, learning was extremely rapid, and negative transfer and RI were negligible. The more the competing primed items in the predicted response category, the slower the learning and the greater the RI. If cues and responses were unrelated, learning was very slow, and RI was appreciable. Thus, predictive relations that help stimuli retrieve unique responses greatly alter forgetting in RI paradigms.

The Role of Repetition and Associative Interference in New Semantic Learning in Amnesia: A Case Experiment

The question of whether globally amnesic subjects can learn new semantic (factual) information is controversial. Some students of amnesia believe that they can, others that they cannot. In this article we report an extensive experiment conducted with the amnesic patient K.C. in which we examined the role of repetition and associative interference in his learning of new semantic information. In the course of 8 study sessions distributed over 4 weeks, we taught K.C. novel, amusing definitions of 96 target words (e.g., “a talkative featherbrain—PARAKEET”). We varied systematically the degree of both pre-experimental and intraexperimental associative interference, as well as the amount of study. The results of the experiment showed that K.C. can learn new semantic knowledge, and retain it over a period as long as 30 months indistinguishably from control subjects. The results further showed that the efficacy of such learning depends critically on both repetition of the material and the absence, or minimization, of pre-experimental and intraexperimental associative interference. These findings suggest that the extent to which at least some amnesic patients can acquire and retain new semantic knowledge depends on the conditions under which learning occurs, and that unqualified statements regarding the deficiency or absence of such learning in amnesia are not justified.

Perceptual and conceptual cueing in implicit and explicit retrieval

Subjects saw or heard words in a list (e.g. limerick) and then took two successive tests. The first was a yes/no recognition test in which auditory/visual modality of test words was manipulated orthogonally to the study modality. The second test varied with experimental conditions: subjects produced words to either perceptual (fragment) cues (l- -e-ick) or conceptual cues (What name is given to a lighthearted five-line poem?), under either explicit or implicit retrieval instructions. The major findings were: (a) that regardless of the type of retrieval cue (perceptual or conceptual) the degree of dependency between recognition and cued recall was greater than that between recognition and implicit retrieval; and (b) that modality shifts adversely affected perceptually cued explicit and implicit retrieval, whereas they had no effect either on conceptually cued retrieval or on recognition. These results suggest that the memory system subserving, and the processes involved in, conceptual priming differ from those underlying recognition and perceptual priming.

Pharmacology of human memory and cognition: illustrations from the effects of benzodiazepines and cholinergic drugs

The current research methods, findings and questions that are being addressed in studies of the pharmacology of human memory and cognition are reviewed. Memory is not a unitary function. Neuropsychological studies of brain-damaged memory-impaired patients, as well as neuroimaging and drug studies in normal individuals indicate that different forms of learning and memory are subserved by different brain systems. Animal drug studies have also provided evidence that, while distinct, memory systems are not independent, but operate in close interaction with one another. Recent human studies of benzodiazepines and of cholinergic drugs demonstrate the value of the psychological models and of the experimental paradigms that are available from cognitive sciences for exploring how drugs alter cognitive and memory functions. They also show how drugs can be used as tools for analyzing the distinct neurochemical mechanisms underlying independent cognitive processes, and so find effective drugs rationally from a knowledge of the neurochemical bases of cognition. This research leads to specific recommendations concerning treatments that may improve memory functioning, for instance in Alzheimer's disease.

Long-lasting perceptual priming and semantic learning in amnesia: A case experiment

An investigation of perceptual priming and semantic learning in the severely amnesic subject K.C. is reported. He was taught 64 three-word sentences and tested for his ability to produce the final word of each sentence. Despite a total lack of episodic memory, he exhibited (a) strong perceptual priming effects in word-fragment completion, which were retained essentially in full strength for 12 months, and (b) independent of perceptual priming, learning of new semantic facts, many of which were also retained for 12 months. K.C.'s semantic learning may be at least partly attributable to repeated study trials and minimal interference during learning. The findings suggest that perceptual priming and semantic learning are subserved by two memory systems different from episodic memory and that both systems (perceptual representation and semantic memory) are at least partially preserved in some amnesic subjects.

Priming and human memory systems

Priming is a nonconscious form of human memory, which is concerned with perceptual identification of words and objects and which has only recently been recognized as separate from other forms of memory or memory systems. It is currently under intense experimental scrutiny. Evidence is converging for the proposition that priming is an expression of a perceptual representation system that operates at a pre-semantic level; it emerges early in development, and access to it lacks the kind of flexibility characteristic of other cognitive memory systems. Conceptual priming, however, seems to be based on the operations of semantic memory.

Contingent dissociation between recognition and fragment completion: the method of triangulation

Two experiments conforming to the logic of the method of triangulation were conducted. Following the study of a list of words, the first of two successive tests (recognition) was identical for two groups of subjects, but the second one, in which the same word-fragment cues were presented to both groups, differed with respect to retrieval instructions. Subjects in one group engaged in cued recall of study-list words, whereas those in the second group completed the fragments with the first word that came to mind. Both experiments yielded the same result: The dependency between the first and second tests, indexed by Yule's Q statistic, was greater for recognition and cued recall than it was for recognition and fragment completion. These results speak to the controversial issue of the usefulness of contingency analyses of data from successive memory tests. The results are interpreted in a theoretical framework consisting of an integration of the idea of a hypothetical quasi-memory system with the transfer-appropriate procedural approach.

Contingent dissociation between recognition and fragment completion: The method of triangulation

Two experiments conforming to the logic of the method of triangulation were conducted. Following the study of a list of words, the first of two successive tests (recognition) was identical for two groups of subjects, but the second one, in which the same word-fragment cues were presented to both groups, differed with respect to retrieval instructions. Subjects in one group engaged in cued recall of study-list words, whereas those in the second group completed the fragments with the first word that came to mind. Both experiments yielded the same result: The dependency between the first and second tests, indexed by Yule's Q statistic, was greater for recognition and cued recall than it was for recognition and fragment completion. These results speak to the controversial issue of the usefulness of contingency analyses of data from successive memory tests. The results are interpreted in a theoretical framework consisting of an integration of the idea of a hypothetical quasi-memory system with the transfer-appropriate procedural approach.

Priming of semantic autobiographical knowledge: a case study of retrograde amnesia

The case of a 36-year-old man who suffers dense retrograde and anterograde amnesia as a result of closed-head injury that caused extensive damage to his left frontal-parietal and right parieto-occipital lobes is described. Patient K.C. has normal intelligence and relatively well-preserved perceptual, linguistic, short-term memory, and reasoning abilities. He possesses some fragmentary general knowledge about his autobiographical past, but he does not remember a single personal event or happening from any time of his life. He has some preserved expert knowledge related to the work he did for 3 years before the onset of amnesia, although he has no personal recollections from that period. Some features of K.C.'s retrograde amnesia can be interpreted in terms of the distinction between episodic and semantic memory, and in terms of the distinction between episodic and semantic autobiographical knowledge. K.C.'s semantic knowledge, but not his episodic knowledge, showed progressive improvement, or priming, in the course of the investigation.

Learning and retention of computer-related vocabulary in memory-impaired patients: method of vanishing cues

Several investigators have suggested that microcomputers might serve as useful external aids for memory-impaired patients. However, knowledge of basic computer vocabulary may be necessary for patients to use and benefit from a microcomputer. The present paper describes a procedure, the method of vanishing cues, which facilitated the acquisition of computer-related vocabulary in four memory-impaired patients. The method involves the systematic reduction of letter fragments of to-be-learned words across trials. Although learning was slow and strongly dependent on first-letter cues, all patients acquired a substantial amount of the vocabulary and eventually were able to produce the target words in the absence of fragment cues. Further, they retained the vocabulary over a 6-week interval and showed some transfer of the knowledge they had acquired. These findings suggest that memory-impaired patients may eventually be able to use a microcomputer as a prosthetic device.