Brendon O. Watson

Network Homeostasis and State Dynamics of Neocortical Sleep

Sleep exerts many effects on mammalian forebrain networks, including homeostatic effects on both synaptic strengths and firing rates. We used large-scale recordings to examine the activity of neurons in the frontal cortex of rats and first observed that the distribution of pyramidal cell firing rates was wide and strongly skewed toward high firing rates. Moreover, neurons from different parts of that distribution were differentially modulated by sleep substates. Periods of nonREM sleep reduced the activity of high firing rate neurons and tended to upregulate firing of slow-firing neurons. By contrast, the effect of REM was to reduce firing rates across the entire rate spectrum. Microarousals, interspersed within nonREM epochs, increased firing rates of slow-firing neurons. The net result of sleep was to homogenize the firing rate distribution. These findings are at variance with current homeostatic models and provide a novel view of sleep in adjusting network excitability.

Two distinct effects on neurotransmission in a temperature-sensitive SNAP-25 mutant

Vesicle fusion in eukaryotic cells is mediated by SNAREs (soluble N‐ethylmaleimide‐sensitive factor attachment protein receptors). In neurons, the t‐SNARE SNAP‐25 is essential for synaptic vesicle fusion but its exact role in this process is unknown. We have isolated a SNAP‐25 temperature‐sensitive paralytic mutant in Drosophila, SNAP‐25ts. The mutation causes a Gly50 to Glu change in SNAP‐25s first amphipathic helix. A similar mutation in the yeast homologue SEC9 also results in temperature sensitivity, implying a conserved role for this domain in secretion. In vitro‐generated 70 kDa SNARE complexes containing SNAP‐25ts are thermally stable but the mutant SNARE multimers (of ∼120 kDa) rapidly dissociate at 37°C. The SNAP‐25ts mutant has two effects on neurotransmitter release depending upon temperature. At 22°C, evoked release of neurotransmitter in SNAP‐25ts larvae is greatly increased, and at 37°C, the release of neurotransmitter is reduced as compared with controls. Our data suggest that at 22°C the mutation causes the SNARE complex to be more fusion competent but, at 37°C the same mutation leads to SNARE multimer instability and fusion incompetence.

Large-scale Recording of Neurons by Movable Silicon Probes in Behaving Rodents

A major challenge in neuroscience is linking behavior to the collective activity of neural assemblies. Understanding of input-output relationships of neurons and circuits requires methods with the spatial selectivity and temporal resolution appropriate for mechanistic analysis of neural ensembles in the behaving animal, i.e. recording of representatively large samples of isolated single neurons. Ensemble monitoring of neuronal activity has progressed remarkably in the past decade in both small and large-brained animals, including human subjects. Multiple-site recording with silicon-based devices are particularly effective because of their scalability, small volume and geometric design. Here, we describe methods for recording multiple single neurons and local field potential in behaving rodents, using commercially available micro-machined silicon probes with custom-made accessory components. There are two basic options for interfacing silicon probes to preamplifiers: printed circuit boards and flexible cables. Probe supplying companies (http://www.neuronexustech.com/; http://www.sbmicrosystems.com/; http://www.acreo.se/) usually provide the bonding service and deliver probes bonded to printed circuit boards or flexible cables. Here, we describe the implantation of a 4-shank, 32-site probe attached to flexible polyimide cable, and mounted on a movable microdrive. Each step of the probe preparation, microdrive construction and surgery is illustrated so that the end user can easily replicate the process.

Sleep, Memory & Brain Rhythms

Sleep occupies roughly one-third of our lives, yet the scientific community is still not entirely clear on its purpose or function. Existing data point most strongly to its role in memory and homeostasis: that sleep helps maintain basic brain functioning via a homeostatic mechanism that loosens connections between overworked synapses, and that sleep helps consolidate and re-form important memories. In this review, we will summarize these theories, but also focus on substantial new information regarding the relation of electrical brain rhythms to sleep. In particular, while REM sleep may contribute to the homeostatic weakening of overactive synapses, a prominent and transient oscillatory rhythm called “sharp-wave ripple” seems to allow for consolidation of behaviorally relevant memories across many structures of the brain. We propose that a theory of sleep involving the division of labor between two states of sleep–REM and non-REM, the latter of which has an abundance of ripple electrical activity–might allow for a fusion of the two main sleep theories. This theory then postulates that sleep performs a combination of consolidation and homeostasis that promotes optimal knowledge retention as well as optimal waking brain function.

Two-photon microscopy with diffractive optical elements and spatial light modulators.

Two-photon microscopy is often performed at slow frame rates due to the need to serially scan all points in a field of view with a single laser beam. To overcome this problem, we have developed two optical methods that split and multiplex a laser beam across the sample. In the first method a diffractive optical element (DOE) generates a fixed number of beamlets that are scanned in parallel resulting in a corresponding increase in speed or in signal-to-noise ratio in time-lapse measurements. The second method uses a computer-controlled spatial light modulator (SLM) to generate any arbitrary spatio-temporal light pattern. With an SLM one can image or photostimulate any predefined region of the image such as neurons or dendritic spines. In addition, SLMs can be used to mimic a large number of optical transfer functions including light path corrections as adaptive optics.

Neuroscience in the Residency Curriculum: The Psychoanalytic Psychotherapy Perspective

Educators of future psychiatrists tend to teach an array of approaches to the mind and brain, including among them the neurobiologic perspective and the psychoanalytic perspective. These may be considered at opposite ends of many spectra, including the fact that psychoanalysis takes a large-scale and treatment-oriented perspective and has helped countless patients over the years, while neuroscience has tended to be reductionistic, focused on understanding, and has helped very few people. A tension, therefore, exists for the educator in teaching neuroscience: is it wise to spend valuable time and energy teaching this interesting but, thus far, impractical field to future practitioners? Here, we argue that neuroscience is re-orienting itself towards more psychoanalytically relevant questions and is likely, in future years, to give new insights into the nature of basic drives and social relations. We additionally argue for balance on the part of providers in both acknowledging biologic underpinnings for clinical phenomena and yet continuing to take a stance oriented towards appropriate change. Given the burgeoning new focus within neuroscience on topics directly relating to the human internal experience and the novel challenges in both understanding those advances and appropriately using them, we encourage educators to continue to give future psychiatrists the educational foundation they need to follow neuroscientific discoveries into the future.

Generation of a semi-dominant mutation with temperature sensitive effects on both locomotion and phototransduction in Drosophila melanogaster

A novel Drosophila mutant named Tripped-and-fell (Taf)) was isolated in a F1 screen for dominant temperature sensitive paralytics. Recombination mapping using multiply marked chromosomes and P elements have pinpointed the locus of Taf to polytene band 93 on the right arm of the third chromosome (3R). When exposed to restrictive temperatures, both Taf heterozygotes and homozygotes paralyzed; however, homozygotes paralyzed at lower temperatures and took longer to recover than heterozygotes. There are also positive correlations between recovery time from paralysis and both duration and temperature of exposure. Electroretinograms (ERGs) revealed that both homozygotes and heterozygotes have a grossly normal light response at 22°C, but at 37°C, the ERGs from both homozygotes and heterozygotes are unable to maintain a normal sustained depolarization and have ar educed off-transient potential. The severity of the ERG repolarization phenotype is greater in homozygotes than in heterozygotes.

PackIO and EphysViewer: software tools for acquisition and analysis of neuroscience data

We present an open-source synchronization software package, PackIO, that can record and generate voltage signals to enable complex experimental paradigms across multiple devices. This general purpose package is built on National Instruments data acquisition and generation hardware and has temporal precision up to the limit of the hardware. PackIO acts as a flexibly programmable master clock that can record experimental data (e.g. voltage traces), timing data (e.g. event times such as imaging frame times) while generating stimuli (e.g. voltage waveforms, voltage triggers to drive other devices, etc.). PackIO is particularly useful to record from and synchronize multiple devices, for example when simultaneously acquiring electrophysiology while generating and recording imaging timing data. Experimental control is easily enabled by an intuitive graphical user interface. We also release an open-source data visualisation and analysis tool, EphysViewer, written in MATLAB, as well as a module to import data into Python. These flexible and programmable tools allow experimenters to configure and set up customised input and output protocols in a synchronized fashion for controlling, recording, and analysing experiments.