How does the visual cortex learn to “see” and interpret visual information from the outside world? How is information stored in the brain? After all, the brain has no central processing unit to control actions and no memory storage banks to keep track of information. There is only a vast network of interconnected neurons.

Today, there is good evidence in support of the notion that learning and memory occur at the synaptic connections that exist between neurons of the brain. The idea is that events in the outside world cause particular patterns of activity in populations of neurons in the cortex. In turn, these activity patterns bring about changes in connective strengths among cortical neurons. Such changes, which are known under the name of synaptic plasticity, are a means of storing information in neuronal circuits. Synaptic plasticity may thus ensure that subsequent presentations of similar although perhaps non-identical stimuli elicit more or less the same activity patterns, thus resulting in a form of recall and detection mechanism.

It follows then that to understand how the brain works, it is essential to understand the properties, the mechanistic underpinnings, and the functional impact of synaptic plasticity in the brain. My lab focuses on the synaptic plasticity learning rules of neocortex. In particular, my group investigates Spike-Timing-Dependent Plasticity (STDP) in visual cortical microcircuits. In the STDP learning paradigm, whether synaptic strengthening and weakening is brought about depends critically on the relative millisecond timing of spiking activity in connected pairs of cells (Fig. 1). Although the precise outcome depends on the brain region that is investigated, typically pre before postsynaptic spiking activity repeated within a couple of tens of milliseconds results in synaptic strengthening, whereas the opposite temporal order evokes weakening of synaptic connections (Fig. 1).

To understand synaptic plasticity in visual cortical circuits, my lab employs several state-of-the-art approaches: quadruple whole-cell recordings (Fig. 2 and animation above), two-photon laser scanning microscopy of synaptic calcium signals (Fig. 3), and computer simulations.

Our research is not limited to the mechanisms and impact of STDP; indeed, several forms of plasticity do not depend on global spikes but on local dendritic spikes. In addition, we cover topics such as cortical circuit connectivity patterns, neocortical information storage, and the impact of synaptic plasticity in vivo. My group also collaborates with researchers both at UCL as well as internationally.