Ilan Lampl's Lab

 Research Lab members Publications Contact information Positions available 

Spontaneous membrane potential of a neuron in the somatosensory cortex of awake, head-fixed rat (~2 seconds, sweeping in real time, with spikes cut at -30 mV).

Local cortical networks consist of feedforward and feedback circuits, found within and across layers. Little is known, however, about their functional role in the processing of sensory inputs. Which kinds of transformations occur in each cortical layer? Do the local recurrent connections amplify distal inputs? What is the role of cortical inhibition in determining the shape of response to an input? How the cortical circuits are affected by adaptation? How inputs arriving from different parts of a receptive field are integrated? Unveiling the mechanisms that generate cortical activity is a crucial step towards understanding information processing in the cortex. To address these questions we study in-vivo the subthreshold and firing properties of neurons in the barrel cortex of the rat.

Primary sensory areas provide a unique opportunity to study how the cortical column is activated. Sensory inputs from the thalamus activate primarily neurons in layer 4 and subsequently the response spreads to other cortical layers and to neighboring columns. Because each neuron in the cortex receives inputs from many local and distal excitatory and inhibitory neurons, the membrane potential of a cortical neuron in the living animal reflects the sum of synaptic activity in the circuits to which the neuron belongs. Firing, however, is evoked only when the activity reaches a threshold.  Hence, our main experimental technique is to record the membrane potential of cortical neurons in-vivo during spontaneous and evoked activity.

The main focus of our lab is to find out how sensory input is processed in different layers of the somatosensory cortex (S1) of the rat. Rats are nocturnal animals with relatively poor sight, so that the whiskers are one of their primary means for gathering information on their environment, performed by repeated sweeps at frequencies of 5-20 Hz. Neurons of layer 4 in S1 of the rat are aggregated into cell clusters termed barrels. The barrels are arranged in rows and columns that correspond topographically to the mystacial whisker pad and thus respond preferentially to one whisker (the principle whisker).

Sensory adaptation:  The response of neurons to natural stimulation depends on the past history of stimulation. Sensitivity increases during periods of weak stimulation, whereas when the background stimulation is strong the sensitivity is reduced. This form of gain control is called sensory adaptation. Our research is focused on the mechanisms of adaptation in the cortex and the thalamus. We have found that cortical adaptation is highly specific to the stimulated whisker and thus indicate that inputs from different whiskers undergo independent adaptation paths. We also study how adaptation affects the balance between excitation and inhibition. Our data provide direct indication for faster adaptation rate of inhibition, when compared to excitation.

Synchrony of cortical activity: Using dual intracellular recordings it was previously shown that the membrane potential of nearby cortical cells in the visual cortex of anesthetized cats is highly synchronized. Similar behavior is found in the barrel cortex of the rat. We utilize this technique to investigate the real-time relation between excitation and inhibition during ongoing activity and during sensory evoked response. Our recently obtained data indicate that the excitatory network is under continuous control of inhibition.

Spatial integration: spatial integration, the process by which different elements of an object that activates a neuron are summed, is fundamental to all sensory modalities. We have found that summation is sublinear and usually the size of the evoked synaptic potential when two whiskers are stimulated simultaneously is almost equal to the larger of the two individual responses.

The olivocerebellar system: In addition to investigating the somatosensory cortex, we also study the cerebellar system, currently focusing on the physiology of the inferior olive (IO) nucleus. We recently demonstrated that neurons in the IO exhibit two types of subthreshold rhythms: at ~10 Hz (the reminiscent of similar activity previously shown in slices) and an additional rhythm at 0.5-2 Hz. Our main interest is to determine the role of this activity type in integration of synaptic inputs in the olivocerebellar system.