There is considerable evidence that the hippocampal system contributes both to (1) the temporary maintenance of memories and to (2) the processing of a particular type of memory representation. The findings on amnesia suggest that these two distinguishing features of hippocampal memory processing are orthogonal. Together with anatomical and physiological data, the neuropsychological findings support a model of cortico-hippocampal interactions in which the temporal and representational properties of hippocampal memory processing are mediated separately. We propose that neocortical association areas maintain shortterm memories for specific items and events prior to hippocampal processing as well as providing the final repositories of long-term memory. The parahippocampal region supports intermediate-term storage of individual items, and the hippocampal formation itself mediates an organization of memories according to relevant relationships among items. Hippocampal-cortical interactions produce (i) strong and persistent memories for events, including their constituent elements and the relationships among them, and (ii) a capacity to express memories flexibly across a wide range of circumstances.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0140525X00035391

Two functional components of the hippocampal memory system

The present study attempts to extend recent research on the relation between hoarding and obsessive-compulsive experiences. In both college student and community samples, hoarding was associated with higher scores on the Yale-Brown Obsessive-Compulsive Scale (YBOCS). The relationship was stronger among the community sample, in which there was a greater range of compulsive symptoms and hoarding behavior. Hoarding was also associated with higher levels of general psychopathology as measured by the Brief Symptom Inventory but not by the Obsessive-Compulsive Personality Disorder subscale from the Millon Clinical Multiaxial Inventory-II or by a measure of ordinary risk taking. Among a sample of patients with obsessive-compulsive disorder (OCD), 31% reported hoarding obsessions and 26% reported hoarding compulsions on the YBOCS symptom checklist. These frequencies are similar to those found elsewhere and suggest that, although not as frequent as the classical symptoms of OCD, hoarding is a common symptom among OCD patients.

Hoarding and obsessive-compulsive symptoms.

Eight pigeons were trained and tested in a simultaneous same/different task. After pecking an upper picture, they pecked a lower picture to indicate same or a white rectangle to indicate different. Increases in the training set size from 8 to 1,024 items produced improved transfer from 51.3% to 84.6%. This is the first evidence that pigeons can perform a two-item same/different task as accurately with novel items as training items and both above 80% correct. Fixed-set control groups ruled out training time or transfer testing as producing the high level of abstract-concept learning. Comparisons with similar experiments with rhesus and capuchin monkeys showed that the ability to learn the same/different abstract concept was similar but that pigeons require more training exemplars.

Same/different abstract-concept learning by pigeons.

Differential responding to changes in the stimulus situation, long central to the concept of stimulus control, also provides the implicit conceptual basis for assessing the nature of a variety of associative relationships. However, there is substantial evidence that the perception of stimulus similarity is not a static property. Generalization gradients to contextual as well as discriminative stimuli flatten over time, and this increase in perceived similarity presumably reflects forgetting of the detailed characteristics or attributes of stimuli. Methodologically, the flattening of the gradient imposes an important constraint: The effect of a stimulus shift will be highly sensitive to the length of the delay interval between training and testing. Conceptually, the loss of memory for stimulus attributes also implies that the sources of interference in retention can increase over time.

Forgetting of stimulus attributes: methodological implications for assessing associative phenomena.

Mechanisms of same/different concept learning in primates and avians

Contents: Part I:Models of Neural Associativity. G. Lynch, R. Granger, U. Staubli, Long-Term Potentiation and the Structure of Memory. T.J. Teyler, A Model of Associative Interactions Mediated by N-Methyl-D-Aspartate Activation. Part II:Long-Term Potentiation in the Hippocampus. P. Andersen, Parameters Controlling the Induction of Long-Term Potentiation. W.C. Abraham, D.K. Bilkey, E.W. Kairiss, Long-Term Potentiation and Local Circuits in the Hippocampus. G. Buzsaki, F.H. Gage, Long-Term Potentiation: Does It Happen in the Normal Brain? When and How? Part III:EEG States and Memory. R.J. Racine, The Kindling Phenomenon: Epilepsy Model or Memory Model? (and Other Areas of Controversy). N. McNaughton, The Role of Hippocampal RSA: Spatial Memory Versus Anxiety. Part IV:Memory Disorders. R.G. Knight, B.E. Longmore, What Is an Amnesic? H.J. Markowitsch, Memory Disorders After Diencephalic Damage. J.A. Ogden, S. Corkin, Memories of H.M. Part V:Memory Models and Processes. W.E. Hockley, Interrogating Memory: A Decision Model for Recognition and Judgment of Frequency. A.A. Wright, Concept Learning by Monkeys and Pigeons. D.C. McCarthy, J.A. Nevin, The Consequences of Remembering. Part VI:Mechanisms of Nonhuman Memory. W.K. Honig, Structure and Function in the Spatial Memory of Animals. P.J. Urcuioli, A Search for Anticipatory Codes in Pigeon Working Memory.

K. Geoffrey White

Papers

Memory Mechanisms: A Tribute To G.v. Goddard