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Prof. Dr. Hans-Peter Thier
Organization: Werner Reichardt Centre for Integrative Neuroscience / Hertie Institute for Clinical Brain Research
Phone number: +49 (0)7071 29 83057
Department: Dept. of Cognitive Neurology
Area: CIN Staff, Steering Committee
Field of Research
The Sensorimotor Laboratory at the Department of Cognitive Neurology focuses on the role of the cerebellum and its interaction with a number of brainstem nuclei and distinct regions of cerebral cortex. It currently pursues three main interests that reflect different aspects of movement control and spatial orientation: the optimization of motor behaviour by learning; the consequences of movement for perception; and the perception of movements for the guidance of social interactions.
A distinctive feature of cerebellum-based learning, worked out by the group, is its extreme speed, which accommodate behavioural adjustments within seconds. The precision and speed of the adjustments allows for compensation in imperfections of movements due to fatigue. This notion that cerebellum-based learning’s biological purpose is to compensate for motor or cognitive fatigue has also led the group to suggest a new perspective on cerebellar ataxia, the key deficit of patients suffering from cerebellar disease. Ataxia, characterized by the lack of precision, reduced velocity and increased variance, is an inevitable consequence of the motor system inability to compensate fatigue.
The cerebellum is not confined to optimizing motor behaviour. Research carried out in the lab suggests the cerebellum has an analogous role in allowing sensory systems to deal with the perceptual consequences of movement. In work on the perceptual consequences of ego motion, the laboratory has addressed the perception of smooth pursuit induced retinal slip of the visual background as a model system. Pursuit-induced slip of the visual background does not translate into the perception of the world moving because the cortical system resorts to predicting the visual consequences of pursuit movement in order to eliminate retinal image slip induced by pursuit. Consequently only retinal slip originating in movement in the world gives rise to the perception of visual motion, providing it is adequate. It is the cerebellum that plays a key role in optimizing visual prediction, thereby ensuring that only those parts of visual motion reach consciousness that are not self-induced and therefore behaviourally relevant. Any impairment of the optimization of the prediction will lead to incomplete compensation of pursuit and arguably also of other forms of self-induced retinal image slip, which the afflicted patient experiences as dizziness.
The intricate interplay of movement and perception also matters for the development and maintenance of social interactions. When considering social interactions, we broaden the concept of movement to include our ability to shift our ‘inner eye’ to places and objects of interest. How is it possible to understand the intentions, desires and beliefs of others, in other words to develop a theory of (the other´s) mind (TOM)? Establishing a TOM requires the identification of another person’s focus of attention and an understanding of the purpose of their actions. Attention allows us to select particular aspects of information impinging on our sensory systems, to bring them to consciousness and to choose appropriate behavioural responses. Social signals such as eye or head or body orientation are a particularly powerful class of sensory cues attracting attention to objects of interest to someone else.
The lab is also trying to unravel neuronal mechanisms that produce joint attention. The working hypothesis is that joint attention is based on specific parts of cerebral cortex (areas in the superior temporal sulcus (STS)), which extract relevant visual features and allow the characterization of eye and head gaze direction, converting them into spatial coordinates according to the prevailing geometrical relationships. It posits that malfunction in these areas may underlie the inability of patients with autism to efficiently exploit gaze cues when interacting with others. Complementary work on the underpinnings of social cognition addresses the role of the mirror neuron system in premotor cortex in action understanding. These are a class of neurons in the monkey premotor cortex that are activated by specific types of goal-directed motor acts such as grasping a piece of apple. Unlike typical motor neurons they are also activated if the animal observes somebody performing similar behaviour. This basic finding has suggested that we may understand the actions of others by mapping observed actions onto our motor repertoire, an idea that is varyingly referred to as simulation or resonance theory. Although these ideas have received wide attention, far beyond the neurosciences, the major tenets of the concept have never been rigorously tested. To better understand the complex features of mirror neurons and ultimately to put the simulation theory to a critical test, the lab is carrying out experiments on premotor cortical area F5. These experiments show that this particular area has access to streams of information (e.g. the operational distance between actor and observer or the subjective value of the action for the observer) that are very important for the evaluation of actions by others. Recent work in the lab clearly shows that observation-related responses of mirror neurons are to some extent viewpoint-invariant, which is significant as we do not see the actions of others from a fixed perspective.
Using short-term saccadic adaptation as a model of motor learning, the lab has been able to develop a detailed model of the neuronal underpinnings of cerebellum based learning. Its central idea is that a climbing fibre signal, representing information on the adequacy of the behaviour prunes a simple spike population signal, which in turn, controls the behaviour.
Caggiano V., Fogassi L., Rizzolatti G., Casile A., Giese M. and Thier P. (2012), Mirror neurons encode the subjective value of an observed action. Proc. Nat. Acad. Sci. 109:11848-11853.
Thier, P. (2011). The Oculomotor Cerebellum. In: Handbook of Eye Movements. S. P. Liversedge, I.D. Gilchrist, S. Everling (Eds.). Oxford University Press. 173- 194.
Prsa M., Dicke P.W. and Thier P. (2010), The absence of eye muscle fatigue indicates that the nervous system compensates for non-motor disturbances of oculomotor function. J. Neurosci. 30:15834-15842.
Caggiano V., Fogassi L., Rizzolatti G., Thier P. and Casile, A. (2009), Mirror neurons differentially encode the peri- and extrapersonal space of monkeys. Science 324: 403-406.
Synofzik M., Lindner A. and Thier P. (2008), The cerebellum updates predictions about the visual consequences of one's behavior. Curr. Biol. 18:814-818.