Parietal cortex and representation of the mental Self

Abstract

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.

Fig. 1.

rCBF distribution in retrieval of previous judgment of mental characteristics, compared with control state. (A) Emergence of self-representation. Differential activity is noted in medial prefrontal and parietal/posterior cingulate regions, together with bilateral occipital and parietal regions, and a confluent left inferior prefrontal and temporal region (P < 0.05, corrected for multiple comparisons). (B) Emergence of representation of Other (Queen). Activation of nearly similar regions. (C) The relative contributions of two of the above regions are, however, different. For Self (Left), activity is comparatively high in right parietal region and low in left lateral temporal region (P < 0.001, uncorrected). (Insets) Left = right hemisphere.

Fig. 2.

rCBF differences (%) from global CBF in sites of peak activity for Self, Best Friend, and Queen. For right inferior parietal region, the site is the voxel of maximal activity during the Self condition (x, y, z: 44, -58, 38). The differences between Self vs. Best Friend and Self vs. Queen are both significant (P = 0.021 and 0.0008, respectively). For left medial temporal region, the site is the voxel of maximal activity during the Queen condition (x, y, z: -50, 2, -20). The differences between Self and Best Friend, Best Friend and Queen, and Self and Queen are all significant (P = 0.014, 0.02, and < 0.0001, respectively).

Fig. 3.

Connectivity patterns during combined tasks. The data are shown as z-score maps of synchronous activity in the rest of the brain across conditions with medial prefrontal region (A), and with medial parietal/posterior cingulate region (B). The former is mainly connected with medial parietal/posterior cingulate, left temporoprefrontal region, and left inferior parietal region; the latter is mainly connected with medial prefrontal cortex and bilateral inferior parietal cortices.

Fig. 4.

TMS at medial parietal site (Pz). Retrieval of self-judgment is less efficient with TMS at a latency of 160 ms than at a latency of 0 ms (P = 0.003), suggesting that neural activity at that time after stimulus presentation is particularly important for self-representation. This effect is not seen for retrieval of judgment of Best Friend. The difference between Self and Best Friend is significant (P < 0.05) (for details, see text and Table 5).