No description available.

No description available.

No description available.

No description available.

The astounding capacity for learning ranks among the nervous system’s most impressive features. This thesis comprises studies employing varied approaches to improve understanding, at the level of neural circuits, of the brain’s capacity for learning. The first part of the thesis contains investigations of hippocampal circuitry – both theoretical work and experimental work in the mouse Mus musculus – as a model system for declarative memory. To begin, Chapter 2 presents a theory of hippocampal memory storage and retrieval that reflects nonlinear dendritic processing within hippocampal pyramidal neurons. As a prelude to the experimental work that comprises the remainder of this part, Chapter 3 describes an open source software platform that we have developed for analysis of data acquired with in vivo Ca2+ imaging, the main experimental technique used throughout the remainder of this part of the thesis. As a first application of this technique, Chapter 4 characterizes the content of signaling at synapses between GABAergic neurons of the medial septum and interneurons in stratum oriens of hippocampal area CA1. Chapter 5 then combines these techniques with optogenetic, pharmacogenetic, and pharmacological manipulations to uncover inhibitory circuit mechanisms underlying fear learning. The second part of this thesis focuses on the cerebellum-like electrosensory lobe in the weakly electric mormyrid fish Gnathonemus petersii, as a model system for non-declarative memory. In Chapter 6, we study how short-duration EOD motor commands are recoded into a complex temporal basis in the granule cell layer, which can be used to cancel Purkinje-like cell firing to the longer duration and temporally varying EOD-driven sensory responses. In Chapter 7, we consider not only the temporal aspects of the granule cell code, but also the encoding of body position provided from proprioceptive and efference copy sources. Together these studies clarify how the cerebellum-like circuitry of the electrosensory lobe combines information of different forms and then uses this combined information to predict the complex dependence of sensory responses on body position and timing relative to electric organ discharge.

Not available / text

No description available.

No description available.

Thesis (MTech (Radiography))--Peninsula Technikon, Cape Town, 2003 / Brain Compatible Learning (BCL), as its name suggests, is a type of learning which is aligned with how the human brain naturally learns and develops. BCL offers many different options and routes to learning as alternatives to conventional 'chalk and talk' methodologies. A BCL curriculum is planned to define the structure and content of a programme of learning, but it also provides opportunities for students to participate in activities, which encourage and enhance the development of an active and deep approach to learning. Using BCL approaches in the classroom thus creates both a stimulating and a caring environment for student learning. This project researches a BCL intervention in a Radiation Science course. The use of BCL techniques has tended to have been done predominantly in the social sciences; this research fills an important 'gap' in the research literature by examining how BCL might be implemented in a technical and scientific context. The research was conducted using an adapted Participatory Active Research methodology in which classroom interventions were planned (within a constructive framework), rather than implemented and then reflected on by all participants. The PAR method was supplemented with a series of detailed questionnaires and interviews. The broad findings of this study relate to students' experiences of BCL in Radiation Science in terms of 'process' and 'product" issues. In terms of process, or the methodology of BCL, students' responses were largely positive.

Merging the senses is key to perception, yet how we achieve this remains unclear. New research finds multimodality even in primary sensory areas, but its role is not understood. We address this question by using in vivo 2-photon calcium imaging in awake mice to test several hypotheses about the possible functions primary somatosensory cortex (S1) may subserve in integrating auditory and tactile sensory input. We first test whether S1 encodes pure auditory stimulus identity by training a linear classifier to decode different sounds from S1 activity. We find that decoder accuracy is slightly-but-significantly above chance, suggesting that S1 weakly encodes sounds. We then ask whether S1 encodes specific audio-tactile feature conjunctions by testing decoder performance for distinct combinations of simultaneously-presented auditory and tactile stimuli. We find that accuracy was within chance levels, indicating that sound-evoked suppression of whisker responses is auditory-stimulus non-specific. Subsequently, we test whether passive experience is sufficient to induce either a) Hebbian-like reactivation of tactile stimulus representations by correlated auditory stimuli or b) enhanced mixed selectivity. We find that passive experience results in neither effect. We also find S1’s auditory and audio-tactile encoding properties to be stable in the face of reinforcement conditioning. As part of a separate project, we also present results that reinforcement conditioning enhances encoding of time and temporal surprise in primary somatosensory cortex.