The human brain is a tremendously complex neuronal circuit that we don’t really understand. For example we do not know how sensory information about the world is encoded in neuronal population activity and transformed into a percept.
Moreover, somehow during development all the highly specific connections in the brain are made so that we can function normally. It is clear now that we do not come hard-wired but that interaction with the environment plays a major role in shaping our brain. In particular during critical periods of cortical development, sensory experience shapes the refinement of connections in the brain but after the critical period only limited remodeling (plasticity) is possible.
Altered experience, or injury, during the critical period can lead to abnormal wiring of the brain, which cannot be corrected later (because then the brain is not plastic anymore) (see here, here and here). The fact that only limited plasticity is present after the critical period is a serious problem because it means that one has to diagnose and correct problems early in infancy for normal development to occur.
Of course we all know that we can learn some thing later in life thus we might be able utilize or enhance adult plasticity to reverse developmental abnormalities.
To address all these challenges, we are identifying specific circuits in the brain and trying to understand how they work, how they encode information about the world, and how they can change.
One focus of our research is aimed at figuring out what circuits and mechanisms allow the cortex to develop and be plastic in early life. We previously identified a specific group of neurons present predominantly in the developing brain, subplate neurons, that play a key role in this process. Loss of these neurons prevents cortical development. Current work in the lab is investigating how these neurons control cortical development and how they are integrated in the developing cortical circuitry (see Zhao et al. 2009, Viswanathan et al 2012, Tolner et al 2012, Meng et al. 2014, Viswanathan et al. 2016, Nagode et al. 2017). More details here.
The cortex is a laminated structure that is thought to underlie sequential information processing. Sensory input enters layer 4 (L4) from which activity quickly spreads to superficial layers 2/3 (L2/3) and deep layers 5/6 (L5/6). Sensory responses themselves depend on ongoing, i.e. spontaneous cortical activity, as well as the state and behavioral context of the animal. Receptive field properties of neurons can rapidly and adaptively be reshaped when an animal is engaged in a behavioral task, indicating that encoding of stimuli is dependent on task- or context-dependent state. Responses also depend on ongoing cortical dynamics in a lamina-dependent fashion. However, we do not know how neuronal circuits shape these emergent dynamics within and between laminae, and we do not know which neurons encode which aspect of a sensory stimulus. In a collaborative project, together with Dr. Dietmar Plenz (NIMH) and Dr. Wolfgang Losert (UMd Physics), funded by the NIH BRAIN initiative we use in vivo 2-photon imaging and stimulation technology that allows rapid imaging and stimulation in multiple focal planes and by developing new computational and analysis techniques based on dynamic systems and graph theoretic measures to extract network dynamics at the single neuron and population level. We use these new techniques to investigate the 3D single cell and population activity patterns in the auditory cortex in mice and identify the influence of single neurons relative to the synergistic influence of specific groups of neurons (the crowd) on network dynamics and ultimately behavior of the animal.
Our work already identified the micro-circuitry of L2/3 of auditory cortex (Watkins et al. 2014), the functional micro-architecture of the auditory cortex, and how this architecture can changes (see Bandyopadhyay et al Nature Neuroscience 2010, Winkowski & Kanold 2013, Winkowski et al. 2013, 2017, Kanold et al. 2014). We are also collaborating with Dr. Shihab Shamma’s lab (UMd) which is studying behavioral induced rapid plasticity in ferrets.
Sensory systems do not work in isolation. Moreover, it is well known that visual deprivation (such as blindness) can lead to improved auditory abilities. However the underlying mechanisms that contribute to these “supernormal” abilities are largely unknown. We are interested in investigating what happens to other cortical areas in particular the auditory cortex when visual experience is altered for short time periods. Our results so far show that brief visual deprivations (simulated blindness) alter auditory processing and thalamocortical synapses (Petrus et al Neuron 2014) and intracortical connection in the auditory cortex (Meng et al. 2015, Petrus et al. 2015). Thus some of the changes seen in auditory performance are likely due to changes in the auditory cortex. Moreover seeing changes in thalamocortical connections to auditory cortex is quite surprising as our visual deprivations occur after the critical period and indicate that crossmodal influence seem to be more powerful than unimodal influences in changing cortical circuits. . More details here