@phdthesis{Homola2011,
  author    = {Homola, Gy{\"o}rgy {\´A}d{\´a}m},
  title     = {Functional and Microstructural MRI of the Human Brain Revealing a Cerebral Network Processing the Age of Faces},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-56740},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2011},
  abstract  = {Although age is one of the most salient and fundamental aspects of human faces, its processing in the brain has not yet been studied by any neuroimaging experiment. Automatic assessment of temporal changes across faces is a prerequisite to identifying persons over their life-span, and age per se is of biological and social relevance. Using a combination of evocative face morphs controlled for global optical flow and functional magnetic resonance imaging (fMRI), we segregate two areas that process changes of facial age in both hemispheres. These areas extend beyond the previously established face-sensitive network and are centered on the posterior inferior temporal sulcus (pITS) and the posterior angular gyrus (pANG), an evolutionarily new formation of the human brain. Using probabilistic tractography and by calculating spatial cross-correlations as well as creating minimum intersection maps between activation and connectivity patterns we demonstrate a hitherto unrecognized link between structure and function in the human brain on the basis of cognitive age processing. According to our results, implicit age processing involves the inferior temporal sulci and is, at the same time, closely tied to quantity decoding by the presumed neural systems devoted to magnitudes in the human parietal lobes. The ventral portion of Wernicke's largely forgotten perpendicular association fasciculus is shown not only to interconnect these two areas but to relate to their activations, i.e. to transmit age-relevant information. In particular, post-hoc age-rating competence is shown to be associated with high response levels in the left angular gyrus. Cortical activation patterns related to changes of facial age differ from those previously elicited by other fixed as well as changeable face aspects such as gender (used for comparison), ethnicity and identity as well as eye gaze or facial expressions. We argue that this may be due to the fact that individual changes of facial age occur ontogenetically, unlike the instant changes of gaze direction or expressive content in faces that can be "mirrored" and require constant cognitive monitoring to follow. Discussing the ample evidence for distinct representations of quantitative age as opposed to categorical gender varied over continuous androgyny levels, we suggest that particular face-sensitive regions interact with additional object-unselective quantification modules to obtain individual estimates of facial age.},
  subject      = {Gesicht},
  language  = {en}
}
@phdthesis{Plichta2009,
  author    = {Plichta, Michael M.},
  title     = {Neural correlates of delay discounting: Effects of dopamine bioavailability and implications for attention-deficit/hyperactivity disorder (ADHD)},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-35953},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2009},
  abstract  = {Humans and other animals share choice preference for smaller-but-sooner over later-but-larger rewards, indicating that the subjective value of a reward is discounted as a function of time. This phenomenon referred to as delay discounting (DD), represents one facet of impulsivity which is inherently connected with reward processing and, within a certain range, adaptive. Maladaptive levels, however, can lead to suboptimal decision-making and represent important characteristics of psychopathologies such as attention-deficit/hyperactivity disorder (ADHD). In line with a proposed influence of dysregulated dopamine (DA) levels on impulsivity, neural structures involved in DD (the ventral-striatum [VS]; orbitofrontal cortex [OFC]) are highly innervated by dopaminergic neurons. However, studies explicitly testing the triadic interplay of dopaminergic neurotransmission, impulsivity and brain activation during intertemporal choice are missing. Therefore, the first study of the thesis examined the effect of different DA-bioavailability levels, indicated by a genetic polymorphism (Val158Met) in the gene of the catechol-O-methyltransferase, on the association of delay discounting and OFC activation. OFC response to monetary rewards that varied by delay-to-delivery was recorded with functional near-infrared spectroscopy (fNIRS) in a sample of 49 healthy human subjects. The results suggest a DA-related enhancement in OFC function from low (low DA level) to partial (intermediate DA level) and full (high DA level) reward delay sensitivity. Furthermore, DA-bioavailability was shown to moderate the association of neural reward delay sensitivity and impulsivity: OFC reward delay sensitivity was strongly correlated with impulsivity at intermediate DA-levels, but not at low or high DA-levels where impulsivity was related to delay-independent OFC amplitudes. It is concluded that DA-level should be considered as a crucial factor whenever impulsivity-related brain activation, in particular to reward delay, is examined in healthy subjects. Dysfunctional reward processing, accompanied by a limited ability to tolerate reward delays (delay aversion), has been proposed as an important feature in ADHD putatively caused by striatal hypo-dopaminergia. Therefore, the aim of the second study of this thesis was to examine subcortical processing of reward delays and to test for neural indicators of a negative emotional response to delay periods. Using functional magnetic resonance imaging (fMRI), brain activation in adult patients with ADHD (n=14) and healthy control subjects (n=12) was recorded during the processing of immediate and delayed rewards. Compared with healthy control subjects, hyporesponsiveness of the VS reward system was evident in patients with ADHD for both immediate and delayed rewards. In contrast, delayed rewards evoked hyperactivation in the dorsal caudate nucleus and the amygdala of ADHD patients, corroborating the central predictions of the delay aversion hypothesis. In combination both studies support the conception of a close link between delay discounting, brain activation and dopaminergic neurotransmission. The results implicate that studies on neural correlates of DD have to account for the DA-bioavailability level and for a negative emotional response to reward delays.},
  subject      = {Impulsivit{\"a}t},
  language  = {en}
}