Research topics
Research methods
•  Extinction
•  Apraxia
                                                  Research Topics  
Spatial Neglect
Spatial neglect is a possible consequence of right-hemisphere brain damage and is characterised by a dramatic failure to orient toward, explore and respond to stimuli presented on the contralesional side, even when these items appear in isolation or for sustained periods of time. For example, neglect patients often only talk to people on their right and fail to eat food from the left side of their plate. Interestingly, while neglect patients fail to respond to certain regions of space, primary sensory loss is not the main cause of neglect. In other words, neglect represents a failure to perceive despite intact sensory processing. In this lab we study the causal mechanisms and neural basis of this neuropsychological syndrome using functional MRI, TMS and behavioural studies in both neurological healthy subjects and neurological patients.
Exploration_of_space_2.jpg, 85kB

- Karnath H-O (2015). Spatial attention systems in spatial neglect. Neuropsychologia 75: 61-73.
- Li D, Rorden C, Karnath H-O (2017). ‘Nonspatial’ attentional deficits interact with spatial position in neglect. J Cog Neurosci: in press.

Classical theories of selective attention have assumed a single focus of attention. In everyday life, however, we are more typically confronted with rapidly changing dynamic scenes that require us to attend simultaneously to multiple non-contiguous spatial locations (for example traffic scenes). The importance of this ability to simultaneously attend to multiple spatial locations is dramatically illustrated in neurological patients suffering from extinction. Extinction is a common consequence of unilateral, most frequently right hemispheric brain damage where patients are able to detect both ipsi- and contralesional information presented in isolation, but are unable to attend and respond to contralesional information in situations where ipsilesional information is concurrently present. Using a combination of fMRI, TMS, lesion-symptom mapping and psychophysical methods in neurologically healthy subjects and neuropsychological patients, we investigate the mechanisms and anatomy that underlie both our ability to attend to multiple spatial locations simultaneously and the disruption of this ability in neuropsychological populations.

- de Haan B, Bither M, Brauer A, Karnath H-O (2015). Neural correlates of spatial attention and target detection in a multi-target environment. Cerebral Cortex 25: 2321–2331.
- de Haan B, Stoll T, Karnath H-O (2015). Early sensory processing in right hemispheric stroke patients with and without extinction.Neuropsychologia 73: 141–150.

Auditory Localization
Despite the movements of eyes, head, and body, a healthy person perceives its environment as a constant visual and acoustical unit. Humans also show a remarkable ability to attend to and localise sounds. By means of functional MRI, we search for the neural correlates underlying these mechanisms. Likewise, in a soundproof room behavioral studies are carried out to clarify the mechanisms of auditory localisation in multisound environments. Our studies are carried out with healthy subjects as well as stroke patients.

- Zündorf IC, Karnath H-O, Lewald J (2014). The effect of brain lesions on sound localization in complex acoustic environments. Brain 137: 1410-1418.
- Zündorf IC, Lewald J, Karnath H-O (2016). Testing the dual-pathway model for auditory processing in human cortex. NeuroImage 124: 672–681. 

Stroke patients may exhibit the peculiar behavior of actively pushing away from the non-hemiparetic side leading to lateral postural imbalance and a tendency to fall towards the paralyzed side. This phenomenon has been called the "Pusher Syndrome". We investigate the cognitive, visual, and vestibular contributions to understand the mechanism leading to contraversive pushing.

                                                      Schematic drawing of pusher patients' perceived postural vertical (SPV) with occluded eyes
                                                                       (A) and while viewing their surroundings (B). The patient's SPV shows a marked ipsiversive
                                                                       deviation from the earth-vertical with occluded eyes.

- Karnath H-O (2007). Pusher syndrome - a frequent but little-known disturbance of body orientation perception. J Neurol 254: 415-24.
- Karnath H-O, Brötz D (2014). Pusher-Syndrom. In: Karnath H-O, Goldenberg G, Ziegler W (eds.) Klinische Neuropsychologie −Kognitive Neurologie. Stuttgart, Thieme, 213-222.

Visual agnosia
Patients with visual agnosia cannot recognise objects in their environment based on visual information. They know everything about such everyday objects and can even verbally describe what they should look like. Patients can even provide quite accurate drawings of typical objects from their memory. Because of their otherwise intact visual input to the brain, these patients are of particular interest for research on visual recognition and the usage and integration of visual information in the human brain. One example is the influential model on visual information processing that has suggested a dissociation between action- and perception-related processing in a dorsal versus ventral stream projection. Appreciating the enormous impetus of this model we scrutinise some of its basic assumptions and postulations, investigating visual agnosia.

- Cornelsen S, Rennig J, Himmelbach M (2016). Memory-guided reaching in a patient with visual hemiagnosia. Cortex 79: 32–41.
- Karnath H-O, Rüter J, Mandler A, Himmelbach M (2009). The anatomy of object recognition – visual form agnosia caused by medial occipitotemporal stroke. Journal of Neuroscience
  29: 5854-5862.

The perception of our environment not only requires the perception of individual objects, but also the integration of multiple objects to a global gestalt (e.g. the integration of individual trees giving rise to the coherent perception of a forest). A holistic perception of complex visual scenes is a crucial aspect of human perception. Patients with brain-damage of the temporo-occipital cortex may show a deficit in global gestalt perception. This deficit has been termed "simultanagnosia". We investigate such patients to reveal the parameters that play a critical role in visual integration and further improve our understanding of the underlying mechanisms. Functional neuroimaging of healthy subjects supplements this research, identifying the role of cortical structures in global Gestalt perception.

- Balslev D, Odoj B, Rennig J, Karnath H-O (2014). Abnormal center-periphery gradient in spatial attention in simultanagnosia. J Cogn Neurosci 26: 2778-2788.
- Rennig J, Himmelbach M, Huberle E, Karnath H-O (2015). Involvement of the TPJ area in processing of novel global forms. J Cogn Neurosci 27: 1587–1600.

Stroke patients with anosognosia for hemiparesis typically are convinced that their limbs function normally although they have obvious motor defects after stroke. They may experience the paretic limbs as strange or as not belonging to them, or even may attribute ownership to another person. Studies suggest that the insular cortex is integral to self-awareness and to one's beliefs about the functioning and the ownership of body parts. We evaluate such phenomena in stroke patients to elucidate the mechanisms leading to anosognosia, the brain structures typically involved when patients exhibit this behaviour, as well as its relation to unilateral spatial neglect.

- Karnath H-O, Baier B (2010). Right insula for our sense of limb ownership and self-awareness of actions. Brain Struct Funct 214: 411-417.
- Baier B, Geber C, Müller-Forell W, Müller N, Dieterich M, Karnath H-O (2015). Anosognosia for obvious visual field defects in stroke patients. Brain Struct Funct 220: 1855-1860.

Body size perception
Body size perception is crucial for our perception of self and also for motion. It is informed by multiple senses, but as yet, it is unclear how the various sources of information are processed and combined. Further, little is known about body size perception in clinical conditions in which body representation is disturbed. In cooperation with the Dept. of Psychosomatic Medicine and Psychotherapy (Prof. Giel / Prof. Zipfel), the Max Planck Institute for Biological Cybernetics (Dr. Mohler / Prof. Bülthoff) and the Max Planck Institute for Intelligent Systems (Prof. Black) we investigate body size perception of healthy and clinical samples in both real world and virtual reality setups.


Optic ataxia
The disorder of optic ataxia, i.e. misreaching of visual targets and faulty scaling of hand aperture while grasping objects, allows for exciting and often surprising insights regarding the anatomy and functionality of the human sensorimotor system. The typical characteristics of this impairment together with its variability in individual patients help us to reveal those cortical areas and networks that are indispensable for rapid and accurate visually-guided limb movements and online movement corrections. Despite its value and importance for the field of action control, research on optic ataxia is addressed by only a few research groups.

- Martin JA, Karnath H-O, Himmelbach M (2015). Revisiting the cortical system for peripheral reaching at the parieto-occipital junction. Cortex 64: 363-379.
- Borchers S, Müller L, Synofzik M, Himmelbach M (2013). Guidelines and quality measures for the diagnosis of optic ataxia. Frontiers in Human Neuroscience 7: 324.

Human action control is characterized by its impressive complexity and flexible adjustment in tool use and object manipulation. We aim to investigate the cognitive control mechanisms involved in in these processes, studying both healthy subjects as well as neurological patients with apraxia. Apraxia is a common consequence of vascular or neurodegenerative defects primarily to the left hemisphere. Apractic patients have deficits in higher skilled movements independent of primary motor skills. They lack the cognitive skills to perform and plan certain actions. Typically affected skills include imitation of gestures, pantomime of object use, or solving of mechanical tasks. Our group studies both the cognitive as well as anatomical basis of this disorder with lesion mapping, fMRI, and behavioral studies.

- Goldenberg G, Karnath H-O (2006). The neural basis of imitation is body part specific. Journal of Neuroscience 26: 6282–6287.
- Schell C, Suchan J, Himmelbach M, Haarmeier T, Borchers S (2014). Limb apraxia in acute ischemic stroke: a neglected clinical challenge? Neurocase 20: 158-162.

Object functionality and mechanical reasoning
Human action control is characterized by its impressive complexity and flexible adjustment in tool use and object manipulation. We aim to investigate the cognitive control mechanisms involved in the evaluation of action affordances associated with an object and their neuronal correlates. How do we recognize an usable tool for a particular technical problem? How do memory and acquired knowledge about tools on the one hand and visual analysis and deductive reasoning on the other hand contribute to our respective decision? A small group of brain-damaged patients are especially impaired in using novel, unfamiliar tools while they are less impaired in using familiar tools. The examination of such patients and further behavioral and neuroimaging studies based on observations in these patients can help us to understand the way different cognitive sources are combined to come up with a motor behavior that no other living species can match.

- Belardinelli A, Barabas M, Himmelbach M, Butz M (2016). Anticipatory eye fixations reveal tool knowledge for tool interaction. Experimental Brain Research 234: 2415–2431.

Impact of object knowledge on visual motor control
We grasp a screwdriver in a specific way if we are about to use it and in a very different way if we just want to put it aside. Despite of such quite obvious dependencies of visual motor control on object recognition, many researchers believe that the actual control of human grasping depends almost entirely on the direct visual information about object sizes irrespective of any stored knowledge in our memory. In contrast, we demonstrated that well established associations, build through a long-term learning process, are powerful enough to change visual motor control. Interestingly, we also observed some patients with impairments in the control of grasping who apparently exploited such associations for an individual improvement: they are better in grasping very familiar in comparison to neutral geometrical objects. Our work suggests that the role of object familiarity on the control of movements was underestimated in the past.

- Borchers S, Verheij R, Smeets JBJ, Himmelbach M (2014). The influence of object height on maximum grip aperture in empirical and modelled data. Journal of Experimental
  Psychology: Human Perception and Performance 40: 889-896.
- Borchers S, Himmelbach M (2012). The recognition of everyday objects changes grasp scaling. Vision Research 67: 8-13.

Human Superior Colliculus
Previous studies have revealed that the superior colliculi play some role in the execution of arm movements. However, the precise functional contribution of the colliculi to the processes of planning and execution and the processing of a movement’s sensory feedback is still unknown. We explore this unknown territory by developing experimental designs that allow for event-related analyses and transfer our paradigms to the ultra-high field 9.4T scanner at the Max Planck Institute for High-field Magnetic Resonance (Prof. Scheffler). Using tensor imaging and resting state fMRI we investigate the connectivity of the superior colliculi within the sensorimotor network.


- Himmelbach M, Linzenbold W, Ilg UJ (2013). Dissociation of reach-related and visual signals in the human superior colliculus. Neuroimage 82: 61–67.
- Loureiro JR, Hagberg GE, Ethofer T, Erb M, Bause J, Ehses P, Scheffler K, Himmelbach M (2017). Depth-dependence of visual signals in the human superior colliculus at 9.4 T. Human
  Brain Mapping 38: 574-587.

                                                                   Research Methods  
Magnetic resonance imaging (MRI)
We use structural magnetic resonance imaging methods (T1,T2 FLAIR, DWI) and diffusion tensor imaging (DTI) to investigate the precise location of brain lesions as well as the structural connectivity between cortical modules and its contribution to both intact and impaired brain function. Finally, we are involved in the development of methodological tools that aid the (semi)automated segmentation of structural magnetic resonance imaging data from neuropsychological populations.

- de Haan B, Clas P, Juenger H, Wilke M, Karnath H-O (2015). Fast semi-automated lesion demarcation in stroke. NeuroImage: Clinical 9: 69–74.
- Suchan J, Umarova R, Schnell S, Himmelbach M, Weiller C, Karnath H-O, Saur D (2014). Fiber pathways connecting cortical areas relevant for spatial orienting and exploration.
  Human Brain Mapping 35: 1031-1043.

Statistical lesion analysis
Using diffusion-weighted (DWI), fluid-attenuated inversion-recovery (FLAIR) magnetic resonance imaging (MRI) as well as spiral computerized tomography (Spiral-CT) scans we identify the lesion location(s) typically associated with specific cognitive disorders. Statistical voxelwise lesion-behaviour mapping (VLBM) is used to determine relationships between behavioral measures/disorders and the location of brain injury, revealing the function of brain regions. Together with Prof. Chris Rorden, University of South Carolina, we improve and develop new VLBM approaches. We also use machine learning algorithms in multivariate pattern analysis as an enhancement to VLBM in the identification of brain networks underlying behavioral disorders. Beyond the neuroscientific identification of human brain function, knowledge of critical brain regions for neurological symptoms can also be used to predict long term post-stroke outcome and thus can support effective therapeutical planning.

- Smith DV, Clithero J, Rorden C, Karnath H-O (2013). Decoding the anatomical network of spatial attention. PNAS 110: 1518-1523.
- Sperber C, Karnath H-O (2017). Impact of correction factors in human brain lesion-behavior inference. Human Brain Mapping: in press.

Normalized perfusion-weighted Imaging (PWI)
In patients with stroke lesions, we use PWI to identify the abnormally perfused brain area(s) that receive enough blood supply to remain structurally intact, but not enough to function normally. In order to recognize these common areas in groups of patients, we analyse the increase of time-to-peak (or TTP) lesion-inducted delays by using spatial normalization of PWI maps as well as symmetric voxel-wise inter-hemispheric comparisons. These new techniques allow comparison of the structurally intact but abnormally perfused areas of different individuals in the same stereotaxic space, and at the same time avoid problems due to regional perfusion differences and to possible observer-dependent biases.

- Karnath H-O, Zopf R, Johannsen L, Fruhmann Berger M, Nagele T, Klose U (2005). Normalized perfusion MRI to identify common areas of   dysfunction: patients with basal ganglia
  neglect. Brain 128: 2462-
- Zopf R, Klose U, Karnath H-O (2012). Evaluation of methods for detecting perfusion abnormalities after stroke in dysfunctional brain regions. Brain Struct Funct 217: 667-675.

fMRI - functional magnetic resonance imaging
fMRI allows to study brain activity in the intact human brain across its whole volume. Most of our fMRI projects are conducted at a 3T Siemens Prisma system located at the University Hospital Tübingen in collaboration with the Department for Biomedial Magnetic Resonance. The available equipment comprises diverse setups for stimulus presentation and response collection including mutliple state-of-the-art eye eye tracker systems, auditory stimulation systems, and MR-compatible video cameras for motion tracking and qualitative observations of participants’ behaviour and performance. Beyond 3T imaging we conduct experiments at the 9.4T Siemens Scanner (see below) in cooperation with the Max Planck Institute for Biological Cybernetics.

High-field Magnetic Resonance
In cooperation with the Max Planck Institute for Biological Cybernetics (Prof. Scheffler) we are exploiting the potential of Ultra High-Field Magnetic Resonance imaging for submillimetre fMRI. The MR system has a field strength of 9.4 Tesla and a usable volume of 60 cm diameter for human studies. The current focus of our research addresses the functional organisation of the human superior colliculi. We aim to establish anatomical sequences that allow us to identify brainstem nuclei with isotropic submillimeter resolution; establish functional sequences to acquire blood oxygen level dependent (BOLD) signals with isotropic submillimeter resolution; and detect BOLD signals to clarify the precise functional contribution of the colliculi to the processes of planning and execution and the processing of a movement’s sensory feedback.

- Loureiro JR, Himmelbach M, Ethofer T, Pohmann R, Martin P, Bause J, Scheffler K, Grodd W, Hagberg G (2018). In-vivo quantitative structural imaging of the human midbrain and the
  superior colliculus at 9.4T. Neuroimage 177: 117-128.

Loureiro JR, Hagberg GE, Ethofer T, Erb M, Bause J, Ehses P, Scheffler K, Himmelbach M (2017). Depth-dependence of visual signals in the human superior colliculus at 9.4 T. Human
  Brain Mapping 38: 574-587.

Transcranial Magnetic Stimulation (TMS)
Transcranial magnetic stimulation (TMS) briefly disrupts ongoing neural processing in a small part of the brain and so can be used to induce a so-called virtual lesion in healthy subjects. This allows us to determine where in the brain neural activity is causally connected to task performance at an excellent temporal and spatial resolution. We use TMS to complement our lesion analysis and fMRI studies and so obtain a more detailed view of the functional architecture of the brain.

- Ritzinger B, Huberle E, Karnath H-O (2012). Bilateral theta-burst TMS to influence global Gestalt perception. PLoS ONE 7: e47820.

Motion tracking
The human brain comprises complex networks to perform action such as grasping, pointing, or object use. These skills can be affected in stroke patients, e.g. patients suffering from optic ataxia or apraxia. To study the human action system, our group uses motion capturing in healthy subjects and neurological patients. VICON Motion Capture Systems can record the position of reflective markers attached to the body or the hand and track movements with high temporal resolution. As the motion capture system does not inhibit subjects with cables, we are also able to study natural movements.

Eye tracking
Our video- and coil-based eye tracking systems allow us to monitor eye movements in both healthy subjects and neurological patients at an excellent temporal and spatial resolution. We use this eye tracking data to make inferences about healthy and pathological attentional processes as well as to monitor fixation during task performance.

- Belardinelli A, Barabas M, Himmelbach M, Butz M (2016). Anticipatory eye fixations reveal tool knowledge for tool interaction. Experimental Brain Research 234: 2415–2431.

Virtual Reality
Immersive virtual reality (VR) allows us to overcome limitations of other approaches and to enhance ecological validity of experimental setups. For example, it enables us to expose participants to a mirror image or even first person perspective of their own visually manipulated body. Together with our collaboration partners at the Max Planck Institute for Biologial Cybernetics we are using portable VR setups that are displayed via a headmounted display (Oculus DK-2) and therefore allow for bedside testing.

Openings Neuropsychologische Ambulanz