Maravall Lab

Research

To make sense of the world around us, the brain must discriminate stimuli that are structured in space and time. Our group explores the principles that make this possible. Recent and ongoing work analyses how different processing stages in a sensory pathway represent and transform information, leading from the raw physical signals that are sampled by sensory receptors to the elaborate stimulus features that underlie sensation, perception and prediction.

We work mainly on the cerebral cortex, the sheet that forms the outer surface of the mammalian brain. Neural circuits in this area underpin perception, decision making and cognition. Diseases that perturb the normal establishment of cortical circuits, such as schizophrenia and autism spectrum disorders, often cause impairments in the transformation and integration of sensory information. In addition to studying the cortex, we also investigate how information is represented in sensory stages that provide input to the cortex, in order to understand the messages that cortical circuitry must process.

Our experimental focus is on a fascinating model system: the whisker pathway of rodents, and particularly its primary sensory cortical area, known as the “barrel cortex” for the particular shape of the clusters of neurons that constitute the first cortical stage for whisker processing.

We use multiple experimental approaches and levels of description.

  • We assess performance on sensory tasks in mice and in humans, allowing us to compare and benchmark animal and human capacities on analogous types of sensory discrimination.
  • We measure neuronal responses using single-cell and population electrophysiological recording and two-photon fluorescence imaging, applied ex vivo in brain slices, and in vivo in animals performing sensory tasks.
  • An important part of our work involves tailoring and applying new analytical tools to extract information from these data. We have applied methods of information theory, dimensional reduction and decoding to sensory responses in the whisker system.

We are always interested in hearing from motivated PhD and postdoctoral candidates, and offer projects within the Sussex Neuroscience 4 year PhD programme and the Leverhulme Doctoral Scholarship Programme 'From Sensation and Perception to Awareness'. We are also currently interested in sponsoring candidates for independent postdoctoral fellowships. Please contact Miguel Maravall for more information.

Whisker responses banner 

Whisker deflections generated at random intervals (top) and a simultaneous recording of a single neuron’s responses in the mouse barrel cortex (bottom). By spiking, this single cell reliably reports whisker deflections that occur after long-enough intervals and provides information about the interval between deflections. Neurons in the barrel cortex convey information about the ongoing stimulus, but relatively weak information about what happened more than a few hundred ms ago. Pitas et al, 2017.

Neurons in the cerebral cortex colour coded according to their response properties

A colour coded map of neurons in the barrel cortex seen from above the cortex and represented relative to the borders of “barrel columns” (dashed lines). Neurons were imaged using a two-photon microscope and fluorescent calcium indicator. Each neuron’s colour represents its preference for a stimulus property (whisker position, velocity, acceleration…); different colours denote selective preference for different stimulus properties. Neurons responding to different properties are interspersed, located near each other – a hallmark of a “salt and pepper” arrangement typical of the rodent cortex. Martini et al, 2017.

Vm entrainment screen capture

A fragment of a stimulus applied to whiskers (top) and recordings of the membrane potential of a single neuron in the rat barrel cortex (bottom) while presenting identical repeats of the stimulus above. Each colour is one repeat; the thick black trace is a mean across repeats. The membrane potential reflects oscillations in brain state but is also modulated by the stimulus, which is sometimes able to reset the brain oscillations and/or lead to a spike. Alenda et al, 2010.

Sequence task schematic

A temporal sequence discrimination task. Making sense of the world demands the ability to discriminate temporally patterned stimuli. To better understand the neuronal processing underlying this capacity, we measure human and mouse performance in a task where vibrations are applied to the fingertip (human) or whiskers (mouse). Target (GO) and non-target (NO-GO) stimuli are composed of “noise” multiplied by a sequence of amplitudes (top). The stimulus to be detected (GO) differs from the NO-GO only in that its temporal patterning over a timescale of ~100 milliseconds is scrambled (note the different ordering of the constituent segments). For both humans and mice, performance averages 70-75% across the population. Bale et al, 2017.