Mental imagery, emotions and ‘literary task sets’
Journal of Consciousness Studies, vol. 19, Nos 7-8, (2012)
The extent to which neural mechanisms for perception and for internal mental images are the same or different has been an area of controversy. The author considers that perception and imagery use the same processes, but do so in response to different signals. Perception is viewed as being driven by bottom-up signals from retinal input via primary and later visual cortices, while mental imagery is driven by top-down signals from the dorsolateral prefrontal and parietal cortices. Studies have shown that in the absence of external stimuli, the prefrontal can activate the inferior temporal region, seen as the final stage in the production of visual representations.
This point is important in the author’s argument, in that he is considering the influence of mental imagery on emotions. At least to some degree, different brain regions, both cortical and subcortical, are involved with different types of emotion. Thus the amygdala is related to fear, the hypothalamus to visceral and hormonal responses, the anterior cingulate to the motivational value of stimuli, the insula to visceral responses and feelings of disgust, and the orbitofrontal to the evaluation of the reward/punisher aspects of sensory inputs.
The author proposes that top-down signals from the dorsolateral prefrontal to the visual cortex causes the visual cortex to send signals to various emotional regions of the brain, altering a subject’s mental state. There is also suggested to be a two-way interaction between the emotional regions and the visual regions. The orbitofrontal, ventromedial prefrontal and amygdala project to the dorsolateral, and the ventral and visual stream, which is involved with the processing of conscious images. The insula also projects to the visual association areas.
It appears that signaling from these areas can enhance processing in the visual cortex and other sensory cortices and also the processing of memory. Emotional intensity of experiences is known to be related to the likelihood of long-term memories being formed. Emotional intensity may also facilitate the recall of memories. The suggestion is that the processing of these areas can be modulated by the emotion-related brain regions. Emotional processing is also considered to influence the direction of attention.
The author is interested in the little researched area of aesthetic preferences in visual and other modalities. The orbitofrontal has come to the fore as an important brain region since the twentieth century taboo on emotion-related research was relaxed. Kawabata and Zeki (2004) (1.) showed in a study that activity in the orbitofrontal correlated with the subjective rating of paintings, leading them to refer to the orbitofrontal as the ‘beauty spot’. Further to this, Ishai (2007) (2.) showed in a study that orbitofrontal activity correlated with the subjective rating of facial attractiveness.
The importance of these papers for consciousness studies is not so much in terms of finding a neural basis for aesthetics, as in terms of the strong suggestion that subjective experience is the product of physical activity in, probably amongst other areas, the orbitofrontal. This is referred to as a correlation, but it would be necessary to propose another unknown factor mysteriously producing subjectivity at the same time as the orbitofrontal activity, if one does not want to accept the orbitofrontal activity as a physical instantiation of consciousness.Tags: mental imagery Posted by