Search PubMed⌕ Search

Biomedical subjects

R P Behrendt

Publications and source records attributed to R P Behrendt.

5 recordsLinked to original sources
PubMed2003

Hallucinations: synchronisation of thalamocortical gamma oscillations underconstrained by sensory input.

What we perceive is the product of an intrinsic process and not part of external physical reality. This notion is consistent with the philosophical position of transcendental idealism but also agrees with physiological findings on the thalamocortical system. gamma-Frequency rhythms of discharge activity from thalamic and cortical neurons are facilitated by cholinergic arousal and resonate in thalamocortical networks, thereby transiently forming assemblies of coherent gamma oscillations under constraints of sensory input and prefrontal attentional mechanisms. Perception and conscious experience may be based on such assemblies and sensory input to thalamic nuclei plays merely a constraining role in their formation. In schizophrenia, the ability of sensory input to modulate self-organisation of thalamocortical gamma activity may be generally reduced. If during arousal thalamocortical self-organisation is underconstrained by sensory input, then attentional mechanisms alone may determine the content of perception and hallucinations may arise.

Cerebral Cortex↗
PubMed1999

Microsatellite instability and loss of heterozygosity in prostatic carcinomas: comparison of primary tumors, and of corresponding recurrences after androgen-deprivation therapy and lymph-node metastases.

BACKGROUND: The molecular mechanisms leading to prostate cancer progression are poorly understood. In particular, those changes which are responsible for androgen-independent growth and metastatic spread in prostate cancer are an issue of current investigations. METHODS: To gain more insight into these processes, paired microdissected samples from both untreated, locally advanced primary tumors (n = 20) and recurrences (n = 20) after conventional androgen-deprivation therapy (ADT) were analyzed retrospectively for microsatellite instability (MSI) and loss of heterozygosity (LOH) at nine loci on chromosomes 8, 18, and X by polymerase chain reaction. In parallel, 12 prostatic carcinomas treated by radical prostatectomy and nine corresponding lymph-node metastases were analyzed in the same way. RESULTS: The group treated with ADT showed a total of 10 MSI in 7 of the primary tumors (35%): 4 of these (20%) at one locus, and 3 of these (15%) at two loci. In the recurrences, MSI was observed in 4 cases (20%): 3 of these at one locus (15%), and 1 of these (5%) at two loci. LOH was found in 8 cases (40%) before as well as after ADT. In the radically resected carcinomas, MSI could be detected at two chromosomal loci in one of the primary tumors (8%) and in one of the metastases (11%); LOH was found in 2 primaries (16%) and 3 metastases (33%). CONCLUSIONS: Although MSI can be found in advanced prostatic carcinomas, it apparently does not play a major role in the progression of prostate cancer regarding androgen-independent growth or lymphogenous spread.

Aged↗
PubMed1996

Cortical simplicity and mental processes.

The cerebral cortex can be looked upon as a non-linear system of coupled oscillators that tries to resist desynchronization and seeks to optimize the activity distribution of its elements. Cortical self-optimization can be disturbed by incoming nervous activity and the cortex will compensate for it by reorganizing the state of the soma, thus producing behavior. This simple concept would not explain mental processes that run within the cortex. It is proposed to relate mental processes to somatic behavior. Emotions, visual images, dreams, thoughts, memories, and anticipations could be perceived from the activity of respiratory, orofacial, and eye muscles. In their basic nature, mental processes may not differ from auditory, visual or visceral sensations. It is the peripheral soma that determines our mind and behavior; the task of the cortex is to line up somatic states. This philosophy could provide a new framework for data and results emanating from different fields of the neuroscience.

Afferent Pathways↗
PubMedDate not supplied

Underconstrained perception: a theoretical approach to the nature and function of verbal hallucinations.

We do not see the world as it is. Perception forms a subjective image of the world in a language that has proven to be adaptive to our interaction with the external world. Perception is mainly determined by current needs of the organism and goals of behavior. Sensory processing itself does not culminate in perception and is not essential for perception, since perception derives from representations of internal symbols and their features. The current stimulation of sensory organs does, however, constrain our perception. Perception might be less constrained by the external world in cases of (1) increased attention, (2) decreased sensory stimulation, or (3) facilitated formation of cortical associations between representations of expectations and internal symbols. Hallucinations are perceptions that are underconstrained by external sensory stimulation. Verbal hallucinations that allow the patient to infer about his self-image might constitute the core psychopathology in a subset of schizophrenia. Commenting and discussing voices might be perceived under the pressure of increased attention to environmental factors that relate to the patient's social fears and wishes. Secondarily, delusions about the possession of thoughts and disorders of self-experience may develop.

Association↗