No abstract

Transcranial magnetic stimulation (TMS) can be applied in different paradigms to obtain a measure of various aspects of cortical excitability. These different TMS paradigms provide information about different neurotransmitter systems, enhance our understanding about the pathophysiology of neuropsychiatric conditions, and in the future may be helpful as a guide for pharmacological interventions. In addition, repetitive TMS (rTMS) modulates cortical excitability beyond the duration of the rTMS trains themselves. Depending on rTMS parameters, a lasting inhibition or facilitation of cortical excitability can be induced. These effects can be demonstrated neurophysiologically or by combining rTMS with neuroimaging techniques. The effects do not remain limited to the cortical area directly targeted by rTMS, but affect a wider neural network transynaptically. Modulation of cortical excitability by rTMS may in the future be useful not only as a research tool but also as a therapeutic intervention in neurology, psychiatry, and neurorehabilitation.

For a coherent and meaningful life, conscious self-representation is mandatory. Such explicit ''autonoetic consciousness'' is thought to emerge by retrieval of memory of personally experienced events (''episodic memory''). During episodic retrieval, functional imaging studies consistently show differential activity in medial prefrontal and medial parietal cortices. With positron-emission tomography, we here show that these medial regions are functionally connected and interact with lateral regions that are activated according to the degree of self-reference. During retrieval of previous judgments of Oneself, Best Friend, and the Danish Queen, activation increased in the left lateral temporal cortex and decreased in the right inferior parietal region with decreasing self-reference. Functionally, the former region was preferentially connected to medial prefrontal cortex, the latter to medial parietal. The medial parietal region may, then, be conceived of as a nodal structure in self-representation, functionally connected to both the right parietal and the medial prefrontal cortices. To determine whether medial parietal cortex in this network is essential for episodic memory retrieval with self-representation, we used transcranial magnetic stimulation over the region to transiently disturb neuronal circuitry. There was a decrease in the efficiency of retrieval of previous judgment of mental Self compared with retrieval of judgment of Other with transcranial magnetic stimulation at a latency of 160 ms, confirming the hypothesis. This network is strikingly similar to the network of the resting conscious state, suggesting that self-monitoring is a core function in resting consciousness.A ll subjective experience may be seen as self-conscious in the weak sense that there is something it feels like for the subject to have that experience. We may at times be selfconscious in a deep way, for example, when we are engaged in figuring out who we are and what we are going to do with our lives, a distinctly human experience giving organization, meaning, and structure to life. In its absence, our representation of ourselves and our world becomes kaleidoscopic and our life chaotic (1).Such explicit ''autonoetic consciousness'' is thought to emerge by retrieval of memory of personally experienced events (episodic memory) (2, 3). The cerebral activation pattern of episodic memory retrieval differs from that of semantic retrieval (retrieval of common knowledge by ''familiarity''): e.g., activation of medial parietal cortex is characteristic of the former and activation of left lateral temporal lobe is characteristic of the latter (4). First, we hypothesize that the cerebral activity pattern of retrieval of previous judgments of a person is determined not only by the episodic retrieval nature of the task, but also by the degree of self-reference of the judgment to be retrieved. Second, we hypothesize that the regions activated by retrieval of judgment of the mental Self are functionally interacting. This network would give a distinc...