Biomedical subjects

Sidney I Wiener

Publications and source records attributed to Sidney I Wiener.

6 recordsLinked to original sources

PubMed2004

Neurons in hippocampal afferent zones of rat striatum parse routes into multi-pace segments during maze navigation.

Hippocampal 'place' neurons discharge when rats occupy specific regions within an environment. This finding is a cornerstone of the theory of the hippocampus as a cognitive map of space. But for navigation, representations of current position must be implemented by signals concerning where to go next, and how to get there. In recordings in hippocampal output structures associated with the motor system (nucleus accumbens and ventromedial caudate nucleus) in rats solving a plus-maze, neurons fired continuously from the moment the rat left one location until it arrived at the next goal site, or at an intermediate place, such as the maze centre. While other studies have shown discharges during reward approach behaviours, this is the first demonstration of activity corresponding to the parsing of complex routes into sequences of movements between landmarks, similar to the lists of instructions we often employ to communicate directions to follow between points on a map. As these cells fired during a series of several paces or re-orientation movements, perhaps this is homologous to 'chunking'. The temporal overlaps in the activity profiles of the individual neurons provide a possible substrate to successively trigger movements required to arrive at the goal. These hippocampally informed, and in some cases, spatially selective responses support the view of the ventral striatum as an interface between limbic and motor systems, permitting contextual representations to have an impact on fundamental action sequences for goal-directed behaviour.

Action Potentials↗

PubMed2004

Rat anterodorsal thalamic head direction neurons depend upon dynamic visual signals to select anchoring landmark cues.

Head direction cells, which are functionally coupled to 'place' cells of the hippocampus, a structure critically involved in spatial cognition, are likely neural substrates for the sense of direction. Here we studied the mechanism by which head direction cells are principally anchored to background visual cues [M.B. Zugaro et al. (2001) J. Neurosci., 21, RC154,1-5]. Anterodorsal thalamic head direction cells were recorded while the rat foraged on a small elevated platform in a 3-m diameter cylindrical enclosure. A large card was placed in the background, near the curtain, and a smaller card was placed in the foreground, near the platform. The cards were identically marked, proportionally dimensioned, subtended the same visual angles from the central vantage point and separated by 90 degrees. The rat was then disoriented in darkness, the cards were rotated by 90 degrees in opposite directions about the center and the rat was returned. Preferred directions followed either the background card, foreground card or midpoint between the two cards. In continuous lighting, preferred directions shifted to follow the background cue in most cases (30 of the 53 experiments, Batschelet V-test, P < 0.01). Stroboscopic illumination, which perturbs dynamic visual signals (e.g. motion parallax), blocked this selectivity. Head direction cells remained equally anchored to the background card, foreground card or configuration of the two cards (Watson test, P > 0.1). This shows that dynamic visual signals are critical in distinguishing typically more stable background cues which govern spatial neuronal responses and orientation behaviors.

Animals↗

PubMed2003

Rapid spatial reorientation and head direction cells.

It is surprising how quickly we can find our bearings when suddenly confronted with a familiar environment, for instance when the lights are turned on in a dark room. Subjectively, this appears to occur almost instantaneously, yet the neural processes permitting this rapid reorientation are unknown. A likely candidate is the head direction (HD) cell system. These limbic neurons found in several brain regions, including the thalamus and the hippocampus, discharge selectively when the head of an animal is oriented in a particular ("preferred") direction. This neuronal activity is independent of position and ongoing behavior and is thus likely to constitute a physiological basis for the sense of direction. Remarkably, although the HD cell system has properties resembling those of a compass, it is independent of geomagnetic fields. Rather, the preferred directions of the HD cells are strongly anchored to visual cues in the environment. Here, we bring evidence for the first time that a fundamental component of the capacity to rapidly reorient in a familiar environment may be brought about by updating of HD cell responses as rapidly as 80 msec after changes in the visual scene. Continuous attractor networks have been used successfully to model HD cell ensemble dynamics. The present results suggest that after large rotations of the surrounding landmarks, activity in such networks may be propagated in abrupt jumps rather than in a gradually progressive manner.

Action Potentials↗

PubMed2002

Peak firing rates of rat anterodorsal thalamic head direction cells are higher during faster passive rotations.

Head direction cells discharge selectively when the head of the animal is oriented in a specific direction. The goal of this study was to determine how sensory signals arising from passive rotations (e.g., triggered by vestibular stimulation and dynamic visual inputs) influence the responses of anterodorsal thalamic head direction cells in the absence of voluntary movement cues (e.g., motor command, efference copy, and associated kinesthetic signals). Three unrestrained rats consumed water from a reservoir at the center of a circular platform while passively subjected to sinusoidal rotatory oscillations at fast (153 +/- 27 degrees/s, sd) and slow (38 +/- 15 degrees/s) peak velocities. In 14 anterodorsal thalamic head direction cells, the preferred directions, angular response ranges and baseline firing rates remained stable, but the peak firing rates were, on average, 36% higher during the fast rotations (Wilcoxon matched-pairs test, p < 0.001; variation range: +11% to approximately +100%). No cell changed its peak firing rate by less than 10%, while three cells (21%) increased their peak firing rates by more than 50%. The velocity-dependent increase in peak firing rates was similar for left and right rotations, and the skewness of the directional response curves were not significantly different between left and right turns (Wilcoxon matched-pairs tests, n = 14, ns). These results show that sensory signals concerning self-movements modulate the responses of the head direction cells in the absence of active locomotion.

Animals↗

PubMed2002

Multisensory processing in the elaboration of place and head direction responses by limbic system neurons.

This review explores the roles of several sensory modalities in the establishment and maintenance of discharges correlated with head position and orientation in neurons of the hippocampus and associated structures in the Papez circuit. Focus is placed on the integration of signals related to environmental cues and to displacement movements, both of external and internal origin. While the visual, vestibular and motor systems each exert influences, position and head direction signals are nevertheless maintained in the absence of any one of these respective inputs. Context-related changes in hippocampal discharge correlates are also highlighted. These characteristics provide these signals with robustness and flexibility, properties particularly suited for cognitive processes such as contextual processing, memory and planning.

Animals↗

PubMedDate not supplied

Persistent activity in limbic system neurons: neurophysiological and modeling perspectives.

Neural activity persisting for one to hundreds of seconds has been postulated to be a substrate of memory. This review article illustrates examples of such activity in limbic system structures including the hippocampus, postsubiculum, and the anterodorsal thalamus. These neuronal responses include better known correlates with the spatial position as well as with head direction of the animal relative to its environment as well as other lesser known examples. Since head direction responses are greater when the animal is actively moving than when passively rotated, it has been proposed that there might be a general mechanism where the behavioral state of the animal can provide modulatory gating of such persistent signals. This would regulate the relative influence of these signals on downstream structures. Neural network attractor models of the head direction cell system are presented to demonstrate how these responses might originate, as well as the dynamics by which they are updated during movements.

Animals↗