Cortical regulation of selective attention in man. A regional cerebral blood flow study.

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Abstract
These experiments were undertaken to reveal the effect of directing attention toward a specific sensory channel on the cortical activation pattern and to reveal which of the cortical areas may be of particular importance for the control of the direction of attention. [Human] subjects (10) who were simultaneously stimulated with pairs of objects pressed against their palms, pairs of ellipses projected on a screen and pairs of tone rhythms presented to 1 ear were examined. The subjects discriminated the stimuli in 1 modality and ignored the input from the 2 other channels. Their regional cerebral blood flow (rCBF) was measured with the intracarotid 133Xe-injection technique. The rCBF was used as an indicator of the regional cortical metabolism in the 254 cortical regions monitored. When subjects exclusively received and discriminated the described somatosensory stimuli (SOM), auditory stimuli (AUD) or visual stimuli (VIS), the rCBF increased in the visual association cortex (VIS), posterior superior parietal cortex (VIS), parietotemporooccipital cortex (AUD, VIS), right inferior parietal cortex (AUD, VIS), right intraparietal cortex (AUD, VIS), contralateral somatosensory cortex and somatosensory association cortex (SOM), auditory cortex (AUD), auditory association cortex (AUD), midtemporal cortex (AUD), inferior posterior frontal cortex (AUD), frontal eye fields (AUD, VIS), anterior and midfrontal cortex (AUD, VIS), posterior midfrontal cortex (SOM, VIS), superior lateral prefrontal cortex (SOM, AUD, VIS) and superior mesial prefrontal cortex (SOM, AUD, VIS). Apart from exceptions mentioned, all rCBF increases were bilateral. In this experiment, with the exception of the left occipital superior cortex, the left posterior superior parietal cortex and the left posterior midfrontal cortex, the rCBF increased in all these areas plus in the left parietal cortex, no matter on what modality the subjects focused their attention. Voluntary direction of attention toward the visual stimuli enhanced the rCBF further in the visual association cortex, the frontal eye fields and activated the right posterior superior parietal cortex. Direction of attention toward the auditory stimuli enhanced the rCBF further in the auditory association cortex, the midtemporal cortex, the Broca area and the frontal eye fields. Concomitant with the direction of attention from one modality to another, the rCBF changed in the superior lateral part of the prefrontal cortex. The superior mesial part of the prefrontal cortex was particularly strongly activated, compared to the SMS [single modality stimulation] studies. When compared to the SMS studies, there were inhibited rCBF increases in the whole left prefrontal cortex and right parietal cortex but enhanced rCBF increases in left parietal cortex, somatosensory cortex and somatosensory association cortex. Since the primary receptive cortex and immediate associative cortex for all 3 modalities were markedly activated in all 3 modes of selective attention, a priori irrelevant signals were apparently processed, at least preliminarily, but the cortex. Since stimulation was identical in each of the 3 modes of selective attention and since stimulus rates and intensities were identical in the SMS studies and the present study, there apparently existed a task-dependent, selective attention-dependent mechanism which, independently of stimulus rates and intensities, enhanced or inhibited the metabolism in cortical areas in a differential way. This mechanism was called differential tuning. The superomesial part of the prefrontal cortex was assumed to participate in the control of differential tuning.