Learning has also been proposed as an independent facet of reward that may be impaired in conditions associated with anhedonia, but empirical evidence dissociating learning from either "liking" or "wanting" is lacking.Anhedonia has also been used to refer to "affective blunting", "restricted range of affect", "emotional numbing", and "flat affect", particularly in the context of post-traumatic stress disorders. In PTSD patients, scales measuring these symptoms correlate strongly with scales that measure more traditional aspects of anhedonia, supporting this association. Causes
Studies in clinical populations, healthy populations, and animal models have implicated a number of neurobiological substrates in anhedonia. Regions implicated in anhedonia include the prefrontal cortex as a whole, particularly the orbitofrontal cortex (OFC), the striatum, amygdala, anterior cingulate cortex (ACC), hypothalamus, and ventral tegmental area (VTA). Neuroimaging studies in humans have reported that deficits in consummatory aspects of reward are associated with abnormalities in the ventral striatum and medial prefrontal cortex, while deficits in anticipatory aspects of reward are related to abnormalities in hippocampal, dorsal ACC and prefrontal regions. These abnormalities are generally consistent with animal models, except for inconsistent findings with regard to the OFC. This inconsistency may be related to the difficulty in imaging the OFC due to its anatomical location, or the small number of studies performed on anhedonia; a number of studies have reported reduced activity in the OFC in schizophrenia and major depression, as well as a direct relationship between reduced activity and anhedonia.
Researchers also came up with hypotheses that audible thought may result from damage in the right hemisphere, which causes the malfunction of prosodic construction. If this happens, the left hemisphere may misinterpret the patients own thoughts as alien, leading the patients to misconceive their thoughts as coming from another voice. Research
A good amount of the research done has focused primarily on patients with schizophrenia, and beyond that drug-resistant auditory hallucinations. Auditory verbal hallucinations as symptoms of disordered speech
There is now substantial evidence that auditory verbal hallucinations (AVHs) in psychotic patients are manifestations of disorganized speech capacity at least as much as, and even more than, being genuinely auditory phenomena. Such evidence comes mainly from research carried out on the neuroimaging of AVHs, on the so-called "inner" and "subvocal" speech, on "voices" experienced by deaf patients, and on the phenomenology of AVHs. Interestingly, this evidence is in line with clinical insights of the classical psychiatric school (de Clérambault) as well as of (Lacanian) psychoanalysis. According to the latter, the experience of the voice is linked more to speech as a chain of articulated signifying elements than to sensorium itself. Non-psychotic symptomatology
There is on-going research that supports the prevalence of auditory hallucinations, with a lack of other conventional psychotic symptoms (such as delusions, or paranoia), particularly in pre-pubertal children. These studies indicate a remarkably high percentage of children (up to 14% of the population sampled) experienced sounds or voices without any external cause, although "sounds" are not considered by psychiatrists to be examples of auditory hallucinations.