Structural theory divides the mental elements for personal social psychology into the id, ego, and super-ego [1] [2]. The definitions of id, ego, and super-ego may be a little different in different situations according to the needs of use. For the convenience of use in neurobiology while in consistence with other neurobiological terms, the id is defined as the basic instincts including motivation [9], unorganized and unconscious, operating without realism or foresight [1] [2] [9] [10]. The ego develops slowly and gradually, being concerned with selfish behaviors including skills mediating between the urging of the id and the realities of the external world [1] [2] [6] [8], and thus operating on reality. The super-ego is held to be the self-observation, self-criticism and other reflective behaviors or common knowledge including law [1] [2]. Obviously, even though called as structural theory of psychoanalysis, the neurobiological counterparts of id/ego/super-ego are all behavioral or psychological. Table 1 outlines the neurobiological counterparts of id/ego/super-ego.

The most noteworthy trends in recent progressions for neurobiology of structural theory of psychoanalysis have pointed to the underlying brain structures and circuits responsible for the id and ego [6] [8] [9]. With regard to id, some authors suggested that the motivation could be more appropriate to represent id than drive [9], while others pointed to the activation of ascending dopaminergic (DA) systems by pleasure [10]. With regard to ego, some authors suggested that the cortical midline structures (CMS) and the default mode network (DMN) correspond to the neural correlates of selfish ego in schizophrenia [6], while others suggested that the cortical parieto-frontal circuits and DMN correspond to the conscious and unconscious part of ego, respectively [8].

However, these neurobiological progressions are far from satisfactory to demonstrate the structural theory of psychoanalysis. 1) Very few neurobiological progressions have been made related to the super-ego of structural theory. 2) Even though the CMS, DMN and cortical parieto-frontal circuits were suggested to be related to ego [6] [8], it has been demonstrated that their specificity was not high sufficiently [6]. Especially, it is difficult to separate the super-ego or even id away from the brain structures or circuits of ego, which results in difficulty for neurobiology to clarify the interactions and conflicts of id, ego, and super-ego with them. 3) Most of the neurobiological progressions on structural theory have neglected the ascending reticular systems [6] [8] [9], therefore incomprehensive in consideration of related brain structures or circuits. Even though some authors have pointed to the ascending DA systems as related to pleasure [10], they are too few and lack of considering the ego and super-ego.

In contrast, for the topographic theory on depression and anxiety, Cai added the reticular NA, 5-HT and ACh systems to demonstrate the differentiated interactions and conflicts of emotion (unconscious), memory (preconscious), and conscious in waking, SWS and REM sleep, respectively [3], in which the SWS and REM sleep manifested opposite with each other [3] [4] [11] [12], quite comprehensive and detailed in mechanisms.

Accordingly, it is obviously necessary to extend the neurobiological consideration of structural theory of psychoanalysis to more brain structures or circuits, especially including the neglected ascending reticular systems.

The structural theory of psychoanalysis is advantageous in that it depicts the personal social psychology by the interactions and conflicts of id, ego and super-ego, emphasizing the importance of selfishness and its interaction with reality, therefore applicable to schizophrenia [6]. Accordingly, it is herein first adopted the schizophrenia-related ascending DA systems to inspect their regulation on id, ego and super-ego.

With regard to id including motivation, the DA systems are excitatory. As mentioned above, some authors have suggested that the ascending DA should be related to pleasure [10]. Besides, the ascending DA systems have directly been depicted as dopamine motive system [13]. In further, it has been demonstrated that the DA in both ventral tegmental area and substantia nigra could contribute to the regulation of motivation [14]. It was noted that the DA systems innervated and regulated the GABAergic interneurons in the basal ganglia, and could directly disinhibit the motivation [14].

With regard to ego representing selfish behaviors including skills, DA can exert the facilitatory effects as manifested in schizophrenia and procedural memory. On the one hand, if hyperactivation of DA may excessively facilitate the ego, it may thus result in psychotic disease like schizophrenia. Indeed, modern technologies have now been able to demonstrate in consensus that the DA in associative striatum is increased in schizophrenia [15] [16], while dysfunction of DA in other brain regions of schizophrenia remains controversial [16]. On the other hand, acquisition of procedural memory can improve the ability of ego as selfish behaviors and skills. Many lines of evidence have demonstrated that the DA of basal ganglia is required for various procedural learning and memory [17] [18], while some authors have even considered the impairment on some types of procedural memories in Parkinson’s disease as important for classification of procedural memories as memory impairment in hippocampal amnesia [18].

With regard to super-ego representing the many reflective behaviors or common knowledge including law, DA can coordinate the selective attention based on self need. It has been reviewed that both prefrontal cortex and DA are involved in selective attention and working memory [19]. Besides, in the attention-deficit/hyperactivity disorder, DA dysfunction has been considered as one of the important pathological causes [20].

It is necessary to point out that the ascending DA systems from substantia nigra and ventral tegmental area may exert different roles [16]. Accordingly, the effects of DA on id/ego/super-ego of structural theory can only be considered as predominant or gross from both of substantia nigra and ventral tegmental area. Detailed depiction of their effects requires further investigation.

Besides the ascending DA systems, the dementia-related ascending ACh systems are herein also adopted to inspect their regulation on id, ego and super-ego.

With regard to id including motivation, the ACh systems are depressive. Hyper- and hypo-cholinergic states may result in depression and mania respectively [21]. Correspondingly, ACh is mainly excitatory to the limbic activities [22].

With regard to ego as selfish behaviors and skills, ACh can exert some restrictive roles. In the famous working memory consolidation model of Mishkin and Appenzeller, lesions of the ascending ACh systems impaired biochemical consolidation of working memories [23], helping restrict the behaviors by avoidance of failures and improvement of success. Besides, some authors have suggested that downregulation of ACh activity may be relevant to some schizophrenia [24], opposite to that of DA.

With regard to super-ego for reflective behaviors or common knowledge and law, ACh mainly helps activation of them including excitation of relevant words in sentence [25] [26], recall of useful declarative memories [27] [28] [29], pharmacological therapies of dementia, and so on. Gamma bands are subject to modulation by the ascending cholinergic systems [30] [31]. The gamma bands of high frequency have been shown to be associated with the word congruency at sentential level [25] [26]. Likewise, recall of recent declarative memories has as well been shown to be associated with the theta-gamma coupling [27] [28] [29]. On the other hand, it has recently been reviewed that the ACh systems are involved in the pathophysiology and treatment of Alzheimer’s dementia [32].

It is as well necessary to note that the ascending ACh systems may activate various subtypes of receptors. In this regard, the above mentioned effects of ACh on id/ego/super-ego should be considered as predominant or gross. It would require more investigations for depiction of their details.