Past events

The view that the brain computes is a working hypothesis in cognitive and brain sciences. But what does it mean to say that a system computes? What distinguishes computing systems, such as brains, from non-computing systems, such as stomachs and tornadoes? I argue that a "structural" approach to computing cannot account for much of the computational work in cognitive neuroscience. Instead, I offer a modeling account, which is a variant of a "semantic" approach. On this modeling account, the key feature of computing is a similarity between the "inner" mathematical relations, defined over the representing states, and "outer" mathematical relations, defined over the represented states.

Learning to read involves exposure to large amounts of print in a focused period of time during childhood. How does this environmental transition affect cortical circuits for visual perception and shape recognition? I will present data from a developmental study of reading examining the relation between reading skill, cortical function and white matter properties in school age children. Functional properties in area MT+, and white matter properties in temporal callosal fibers, are both correlated with reading skill. I will discuss possible interpretations of these findings within a general model of the reading pathways.

The olivo-cerebellar system plays a crucial role in timing of both motor and non-motor tasks. The mechanisms underlying this timing capability are still unclear. Here I propose a plausible mechanism in which a temporal pattern reflects accurate phase relationships between the oscillatory activity of olivary neurons. I provide evidence from chronic multi-electrode recordings in awake rats that inferior olive oscillations possess hitherto unknown properties that: (1) Oscillations in different parts of the inferior olive can maintain constant, non-zero phase differences; (2) The oscillation frequency of olivary neurons is co-modulated; and (3) Phase differences are well maintained despite frequency changes. Thus, the inferior olive can generate not only “clock ticks” at the oscillation cycle duration, but more importantly shorter intervals that emerge by combining different parts of the olivary circuitry. This enables the olivo-cerebellar circuit to support timing in the range implicated by behavioural studies.

Functional MRI (fMRI) studies have defined a series of visual processing regions in the human cortex, which are believed to enable visual recognition behaviors through a hierarchy of processing stages. At the higher stages in this hierarchy lie regions which preferentially respond to images of intact objects compared to other visual stimuli, a set of regions collectively termed object-selective cortex. Within object-selective cortex exist category-selective regions, which prefer particular categories of images over others (e.g., faces, body parts, houses or scenes). Initially these regions were considered non-retinotopic, but increasing evidence indicates substantial retinal position selectivity, and in some cases retinotopy, in these regions. What is the representation of the visual field in object-selective regions? Are separate object- and category-selective regions part of a single map or embedded within a set of distinct visual field maps? We scanned seven subjects on separate experiments to localize object/category-selective regions, and measure visual field maps (GE 3T scanner). For retinotopic experiments, subjects viewed moving bar stimuli containing different stimuli, including slowly drifting checkerboards and frontal face images. The bars extended out to around 14° eccentricity from the fovea, and had a width of ~2.6°. We employed a recently-developed method for estimating population receptive fields (pRFs) using fMRI (Dumoulin and Wandell, Neuroimage, 2008), which estimates pRF center and size for each cortical location. Face-containing bars produced substantially larger responses than checkerboards along the fusiform gyrus, improving our ability to measure visual field maps in these regions. Eccentricity maps revealed two foveal representations, which may correspond to visual field map clusters previously identified as VO and VT (Wandell et al., Neuro-opth. Jpn., 2006). These foveas are within or adjacent to fusiform face-selective regions, and separated by smoothly-varying extra-foveal maps which are less face-selective. For several subjects, pRF sizes systematically increased with eccentricity in face-selective regions. The distribution of pRF sizes were substantially larger than in earlier visual cortex, but comparable to recent measurements made in lateral occipital cortex. We find two spatially separate face-selective regions along the fusiform gyrus, with comparable visual field coverage, separated by a representation of intermediate eccentricities. This indicates these two regions are likely to fall within different visual field maps. Current work addresses possible effects of low-level visual features (e.g. spatial frequency) and stimulus visibility in driving the observed face-selective retinotopic responses. I will also present some preliminary data from retinotopic mapping with house-containing bars, and an examination of retinotopic organization in house- or scene-selective cortical regions.

Optogenetics, synthesizing microbial opsins and solid-state optics, has achieved the goal of millisecond-precision bidirectional control of defined cell types in freely behaving mammals, but has not yet been widely applied to neuroscience and neuropsychiatry experimental challenges. First, relevant to important basic science questions, we have now successfully developed methods to target and control several classes of modulatory neurons in behaving mammals and intact neural tissue, and we are probing and quantifying measures of altered circuit performance under optogenetic control of defined circuit elements to address longstanding questions about neural circuit dynamics. Second, relevant to neuropsychiatric disease questions, we have used this approach for depth targeting of hypothalamic cells (in this case, the hypocretin/orexin cells in the lateral hypothalamus), establishing for the first time a causal relationship between frequency-dependent activity of genetically defined neurons important in clinical neuropsychiatric disease and a complex orchestrated mammalian behavior. We also are now applying fast optical control and optical imaging to animal models of depression, Parkinson’s Disease, and altered social behavior relevant to autism. Insights into both normal circuit function and disease mechanisms are beginning to emerge from this multidisciplinary technological approach. Prof. Deisseroth is hosted by the students of the Department of Neurobiology, as a part of the departmental students-invited visiting scientist program.

Brain functioning underlies perception of outer objects and supports behavioral responses to environmental challenges. As brain circuits mature in the first 20 years of life, so mental abilities emerge. This talk will examine the relation between brain maturation—synaptogenesis and myelination— and levels of cognitive, moral, and ego development. Learning disabilities, such as ADHD and reading disabilities will be explored in light of associated brain patterns. Effects of experiences on brain functioning will also be examined including effects of restrictive experiences such as stress, drug use and fatigue, and enhancing experiences, such as Transcendental Meditation practice. High levels of human potential will be discussed in terms of enhanced brain functioning.

The amygdala and the medial prefrontal cortex interact to guide emotional behavior. Alterations in the balance between these two structures can lead to persistent fear associations and to the development of anxiety disorders. In this talk I will present work from my laboratory studying the interaction between these two structures in normal conditions and when exposed to a fearful or stressful experience. We have recently found that fear and extinction learning induce differential changes in these two structures that could hint on the mechanisms by which these structures encode memories of fear and safety.