Using the Change Manager Model for the Hippocampal System to Predict Connectivity and Neurophysiological Parameters in the Perirhinal Cortex

Theoretical arguments demonstrate that practical considerations, including the needs to limit physiological resources and to learn without interference with prior learning, severely constrain the anatomical architecture of the brain. These arguments identify the hippocampal system as the change manager for the cortex, with the role of selecting the most appropriate locations for cortical receptive field changes at each point in time and driving those changes. This role results in the hippocampal system recording the identities of groups of cortical receptive fields that changed at the same time. These types of records can also be used to reactivate the receptive fields active during individual unique past events, providing mechanisms for episodic memory retrieval. Our theoretical arguments identify the perirhinal cortex as one important focal point both for driving changes and for recording and retrieving episodic memories. The retrieval of episodic memories must not drive unnecessary receptive field changes, and this consideration places strong constraints on neuron properties and connectivity within and between the perirhinal cortex and regular cortex. Hence the model predicts a number of such properties and connectivity. Experimental test of these falsifiable predictions would clarify how change is managed in the cortex and how episodic memories are retrieved.

Abstract 18368: Evidence for Activation of Cerebral Autonomic Center in Response to Cardiac Electrical Stimulation in Humans -A New Finding of Cardio-Cerebral Connection

Introduction: Anterior cingulate cortex (ACC) is one of the cortical receptive fields of afferent nerves innervating the visceral organs and modulates autonomic nervous system in collaboration with hypothalamus and brainstem. Cardiac afferent nerves are associated with not only chest pain but also sympathetic arousal in heart failure, in which ACC could be involved. However, the cortical receptive fields of cardiac afferent nerves still remain to be elucidated. Hypothesis: We thus investigated whether ACC is activated in response to cardiac electrical stimulation in humans. Methods: We studied 10 patients (74.7±1.9 yrs, M/F 9/1) with cardiac pacemaker implantation. Before the measurement, mode of cardiac pacemaker was changed to VVI 80-90 bpm with 1.5V intensity. Cerebral blood flow (CBF) was measured using [15O]H2O positron emission tomography (PET) during sham stimulation (1.5V) and intense stimulation (7.5-8V). The CBF images of intense stimulation were compared with those of sham stimulation using SPM8, a common analysis tool for neuroimages. Cardiac sensation was evaluated with an ordinate scale after CBF measurements. Blood samples were obtained from the cubital vein before and after CBF measurements for plasma catecholamine levels (one patient was excluded for the analysis due to urination before the last blood sampling). Results: Intense stimulation did not induce cardiac sensation but significantly increased plasma adrenaline levels as compared with sham stimulation (intense, 6.1±1.8 vs. sham, 0.1±3.0 pg/ml, P=0.031, n=9 each). CBF in ACC was significantly increased in response to intense stimulation as compared with sham stimulation (intense, 64.6±0.7 vs. sham, 61.0±1.3 ml/100g/min, P=0.008, n=10 each) ( Figure, yellow arrowhead ). Conclusions: This study demonstrates for the first time that ACC could be the cortical receptive field of cardiac afferent nerves associated with sympathetic arousal in humans.

Signal-Tuned Gabor Functions as Models for Stimulus-Dependent Cortical Receptive Fields

We propose and analyze a model, based on signal-tuned Gabor functions, for the receptive fields and responses of V1 cells. Signal-tuned Gabor functions are gaussian-modulated sinusoids whose parameters are obtained from a given, spatial, or spectral “tuning” signal. These functions can be proven to yield exact representations of their tuning signals and have recently been proposed as the kernels of a variant Gabor transform—the signal-tuned Gabor transform (STGT)—which allows the accurate detection of spatial and spectral events. Here we show that by modeling the receptive fields of simple and complex cells as signal-tuned Gabor functions and expressing their responses as STGTs, we are able to replicate the properties of these cells when tested with standard grating and slit inputs, at the same time emulating their stimulus-dependent character as revealed by recent neurophysiological studies.

Longitudinal in vivo Imaging Reveals Balanced and Branch-Specific Remodeling of Mature Cortical Pyramidal Dendritic Arbors after Stroke

The manner in which fully mature peri-infarct cortical dendritic arbors remodel after stroke, and thus may possibly contribute to stroke-induced changes in cortical receptive fields, is unknown. In this study, we used longitudinal in vivo two-photon imaging to investigate the extent to which brain ischemia can trigger dendritic remodeling of pyramidal neurons in the adult mouse somatosensory cortex, and to determine the nature by which remodeling proceeds over time and space. Before the induction of stroke, dendritic arbors were relatively stable over several weeks. However, after stroke, apical dendritic arbor remodeling increased significantly (dendritic tip growth and retraction), particularly within the first 2 weeks after stroke. Despite a threefold increase in structural remodeling, the net length of arbors did not change significantly over time because dendrite extensions away from the stroke were balanced by the shortening of tips near the infarct. Therefore, fully mature cortical pyramidal neurons retain the capacity for extensive structural plasticity and remodel in a balanced and branch-specific manner.