A simple neural network model of the hippocampus suggesting its pathfinding role in episodic memory retrieval

The goal of this work is to extend the theoretical understanding of the relationship between hippocampal spatial and memory functions to the level of neurophysiological mechanisms underlying spatial navigation and episodic memory retrieval. The proposed unifying theory describes both phenomena within a unique framework, as based on one and the same pathfinding function of the hippocampus. We propose a mechanism of reconstruction of the context of experience involving a search for a nearly shortest path in the space of remembered contexts. To analyze this concept in detail, we define a simple connectionist model consistent with available rodent and human neurophysiological data. Numerical study of the model begins with the spatial domain as a simple analogy for more complex phenomena. It is demonstrated how a nearly shortest path is quickly found in a familiar environment. We prove numerically that associative learning during sharp waves can account for the necessary properties of hippocampal place cells. Computational study of the model is extended to other cognitive paradigms, with the main focus on episodic memory retrieval. We show that the ability to find a correct path may be vital for successful retrieval. The model robustly exhibits the pathfinding capacity within a wide range of several factors, including its memory load (up to 30,000 abstract contexts), the number of episodes that become associated with potential target contexts, and the level of dynamical noise. We offer several testable critical predictions in both spatial and memory domains to validate the theory. Our results suggest that (1) the pathfinding function of the hippocampus, in addition to its associative and memory indexing functions, may be vital for retrieval of certain episodic memories, and (2) the hippocampal spatial navigation function could be a precursor of its memory function.     

Reorientation by geometric and landmark information in environments of different size

It has been found that disoriented children could use geometric information in combination with landmark information to reorient themselves in large but not in small experimental spaces. We tested domestic chicks in the same task and found that they were able to conjoin geometric and nongeometric (landmark) information to reorient themselves in both the large and the small space used. Moreover, chicks reoriented immediately when displaced from a large to a small experimental space and vice versa, suggesting that they used the relative metrics of the environment. However, when tested with a transformation (affine transformation) that alters the geometric relations between the target and the shape of the environment, chicks tended to make more errors based on geometric information when tested in the small than in the large space. These findings suggest that the reliance of the use of geometric information on the spatial scale of the environment is not restricted to the human species.     

Organizational identification as a trigger for personal well-being: Associations with happiness and stress through job outcomes

Recent literature highlights that well-being, happiness, as well as personal stress, has become important for guiding public policy in areas that might involve suboptimal behaviour. Positive life outcomes can extend from one field of life (family, work, sport, children, hobbies, etc.) to another, multiplying success, performance, and health. In the present study, we aimed to verify whether the positive relation between organizational identification and employees' experiences then extends also into a positive association with more general well-being that is unrelated to the work context. For this purpose, we considered two proxies of organizational well-being: job satisfaction (on the positive side) and turnover intention (on the negative side) as well as the distal associations with happiness. The study involved 305 workers who completed a questionnaire made up of five scales: organization identification, job satisfaction, turnover intention, happiness, and personal stress. We found that organizational identification is positively related to employees' job satisfaction and negatively related to their intention to leave. Afterwards, job satisfaction and turnover intention were related to personal stress and happiness, suggesting a positive effect of organizational identification above and beyond the work context.     

Psychophysiological correlates of organizational change and threat of unemployment among police inspectors

The study examined psychosocial work-conditions and physiological reactions among thirty-six police inspectors (median age 45 years, 81% males) who participated in a reorganization. At this time, subjects were threatened by unemployment and had to reapply for their positions in a new police district. Data were collected during the reorganization and at three years follow-up, by means of questionnaires (Stress Profile) and blood samples. The blood samples were used to determine serum levels of gammaglutamyltransferase (GGT), glucose, lipids, prolactin, testosterone and cortisol. The results show a positive association betweenworry about employment and symptoms ofburnout during the reorganization. Mean scores for the Stress Profile sub-scalesworry about employment (p<.01) andwork-load (p<.05) decreased between measurements but an impairment inrelationships with management was noticed (p<.05). No significant changes were observed in terms of self-rated health complaints. Significant decreases in total cholesterol (p<.0001), LDL-cholesterol (p<.0001), LDL/HDL-ratio (p<.01), prolactin (p<.0001), as well as increases in testosterone (p<.01) and cortisol (p<.001) were observed for the whole sample. Glucose decreased with marginal significance (<.07). Controlling for age and gender, multivariate regression analyses showed that subjects who reported deteriorations insatisfaction with work manifested the most modest decreases in prolactin (p<.05). Also, the decrease in glucose was larger for subjects who experienced impairments in,satisfaction with work (p<.05), information (p<.05), task-oriented leadership, (p<.05), andrespect and dignity (p<.05). Subjects who perceived deteriorations in theethical and moral standards of the organization increased their cortisol level to a lower degree than their counterparts (p<.05). Favorable changes in employment status and psychosocial work environment seem to be related to improved physiological functioning.     

Rigid and non-rigid kinetic depth effect with rotating discrete helices

Summary To examine the conditions in which human observers fail to recover the rigid structure of a three-dimensional object in motion we used simulations of discrete helices with various pitches undergoing either pure rotation in depth (rigid stimuli) or rotation plus stretching (non-rigid stimuli). Subjects had either to rate stimuli on a rigidity scale (Experiments 1 and 2) or to judge the amount of rotation of the helices (Experiments 3 and 4). We found that perceived rigidity depended on the pitch of the helix rather than on objective non-rigidity. Furthermore, we found that helices with a large pitch/radius ratio were perceived as highly non-rigid and that their rotation was underestimated. Experiment 5 showed that the detection of a pair of dots rigidly related (located on. the helix) against a background of randomly moving dots is easier at small phases in which the change of orientation across frames is also small. We suggest that this is because at small phases the grouping of dots in virtual lines does occur and that this may be an important factor in the perceived nonrigidity of the helices.This research was supported by MPI 60% (1987, 1988) and CNR (1986), 1987, 1988) grants to Clara Casco and Sergio Roncato and Grant CNR 90.01603.PS93 to Giorgio Ganis.     

Brain, emotion and decision making: the paradigmatic example of regret

Human decisions cannot be explained solely by rational imperatives but are strongly influenced by emotion. Theoretical and behavioral studies provide a sound empirical basis to the impact of the emotion of regret in guiding choice behavior. Recent neuropsychological and neuroimaging data have stressed the fundamental role of the orbitofrontal cortex in mediating the experience of regret. Functional magnetic resonance imaging data indicate that reactivation of activity within the orbitofrontal cortex and amygdala occurring during the phase of choice, when the brain is anticipating possible future consequences of decisions, characterizes the anticipation of regret. In turn, these patterns reflect learning based on cumulative emotional experience. Moreover, affective consequences can induce specific mechanisms of cognitive control of the choice processes, involving reinforcement or avoidance of the experienced behavior.     

Spatial reorientation: the effects of space size on the encoding of landmark and geometry information

The effects of the size of the environment on animals’ spatial reorientation was investigated. Domestic chicks were trained to find food in a corner of either a small or a large rectangular enclosure. A distinctive panel was located at each of the four corners of the enclosures. After removal of the panels, chicks tested in the small enclosure showed better retention of geometrical information than chicks tested in the large enclosure. In contrast, after changing the enclosure from a rectangular-shaped to a square-shaped one, chicks tested in the large enclosure showed better retention of landmark (panels) information than chicks tested in the small enclosure. No differences in the encoding of the overall arrangement of landmarks were apparent when chicks were tested for generalisation in an enclosure differing from that of training in size together with a transformation (affine transformation) that altered the geometric relations between the target and the shape of the environment. These findings suggest that primacy of geometric or landmark information in reorientation tasks depends on the size of the experimental space, likely reflecting a preferential use of the most reliable source of information available during visual exploration of the environment.     

Methodological evolution and clinical application of C.G. Jung's Word Association Experiment: a follow-up study

We became interested in the clinical application of the Word Association Experiment (AE) when we decided to use Jung's theory of complexes in the psycho-diagnostic evaluation and treatment of patients applying to our Psychotherapy Out-patients Unit (Psychiatric Clinic, Milan University). In psychopathological situations, complexes with a particularly high emotional charge become autonomous and disturbing, inhibiting the ego's functions. The representations and affective states corresponding to these complexes become dominant, conditioning the expression of symptoms and the subject's relational modes. In this experimental study we started out from the basic theory that our psycho-therapeutic work should lead to a progressive change in the patient's initial complex set up. Jung's Word Association Experiment allows us to identify those words which indicate and stimulate a specific activation of the complexes for each subject via specific markers of complexes. We therefore decided to determine whether AE, administered during the first phase of clinical-diagnostic evaluation and after one year of treatment, revealed any changes occurring in the patients' set up of complexes.     

Visual perception of biological motion in newly hatched chicks as revealed by an imprinting procedure

Day-old chicks were exposed to point-light animation sequences depicting either a walking hen or a rotating cylinder. On a subsequent free-choice test (experiment 1) the chicks approached the novel stimulus, irrespective of this being the hen or the cylinder. In order to obtain equivalent local motion vectors, in experiments 2 and 3 newly hatched chicks were exposed either to a point-light animation sequence depicting a walking hen, or to a positionally scrambled walking hen (i.e. an animation in which exactly the same set of dots in motion as that employed for the walking hen was presented, but with spatially randomized starting positions). Chicks tested on day 1 (experiment 2) or on day 2 (i.e. after a period in the dark following exposure on day 1 (experiment 3)) proved able to discriminate the two animation sequences: males preferentially approached the novel stimulus, females the familiar one. These results indicate that discrimination was not based on local motion vectors, but rather on the temporally integrated motion sequence. Received: 18 August 1999 / Accepted after revision: 14 March 2000     

On Hierarchical Propositions

Journal of Philosophical Logic - There is an apparent dilemma for hierarchical accounts of propositions, raised by Bruno Whittle (Journal of Philosophical Logic, 46, 215–231, 2017): either...