The brain contains numerous folds and convolutions that make up different anatomical structures, among which is the lower frontal gyrus, which we will discuss in this article .
This brain region is part of the prefrontal cortex, and houses such important areas as Broca’s, which is essential in the production of language.
Below we explain what the lower frontal gyrus is and where it is located, what functions it performs and what are the main disorders associated with injuries in this area of the brain.
Lower front turn: definition, structure and anatomical location
The lower frontal gyrus is one of the many convolutions that the human brain contains ; folds that form the characteristic relief of this organ and that give it that wrinkled aspect to its external surface, the cerebral cortex.
This turn is located under the lower front groove, and extends forward from the bottom of the pre-central groove. It is bounded on the front by the lateral or Silvio’s cleft. Up to three different parts can be identified in the lower frontal gyrus: the opercular pair, behind the anterior ascending branch; the triangular pair, between the ascending and horizontal branches; and the orbital pair, below the anterior horizontal branch of the cleft.
The flow limit of the pars opercularis is the lower precentral groove and its rostral limit is the anterior ascending branch of the lateral cleft . Sometimes, an additional groove is identified: the diagonal groove, within the opercular pairs. When this is present, it may remain separate or may be mixed with the ascending groove.
On the other hand, there are authors who have divided the lower front turn into a rear turn and a front turn. While it is true that this groove can be said to continue, ventrally, almost to the lateral margin of the orbital frontal region, this may be a false impression as a result of the fusion of the anterior part of the lower frontal groove with a different groove that often forms the anterior end of the triangular pair: the pretriangular groove.
The lower frontal gyrus is one of the parts that compose the prefrontal cortex of the brain, whose main functions have to do with executive control and planning of complex behaviors, decision making or management and adaptation of behavior to social norms .
In recent years, research has focused on the role of lower frontal turn in a specific aspect of executive control: behavioural inhibition or response inhibition . This can be defined, in general terms, as the capacity we have to control and retain the responses to routine or predominant internal or external stimuli, which appear during the performance of some task.
Tasks that examine response inhibition usually involve the development of a routine response, followed by cancellation of the response when an infrequent stop signal is detected. For example, with the Go/No go task, in which there are two starting conditions, and in some tests you have to respond to stimuli (Go test) and in others you do not have to respond (No go), so the examiner can then measure the individual’s ability to inhibit his or her responses.
Another function in which the lower front turn would be involved is attentional control. To measure a subject’s attentional capacity, “Stop signal” tasks are usually used, an experimental test that serves to measure inhibitory processes and the automaticity of subjects’ responses, and which also uses Go/No Go tasks.
The latest findings based on functional magnetic resonance studies confirm that the lower frontal gyrus also plays an overall role in attention control as a necessary structure for the person to adapt and respond to relevant stimuli and to inhibit non-relevant or distracting stimuli.
It is also worth noting the role played by the lower frontal gyrus in language processing, since the Broca area is part of this gyrus. This brain region, located in the left hemisphere, is essential in language expression and speech production, as it is responsible for planning the sequence of movements necessary for us to articulate the words we speak.
Mirror neurons are a special class of neurons that are activated both by observing the behavior of others and by executing it ourselves. They are called mirror neurons because they allow us to deduce what others are thinking and feeling, and they are closely related to aspects such as empathy, imitation or social behaviour.
There is evidence that there are mirror neurons in various brain regions, including: the pars opercularis of the inferior frontal gyrus and the inferior parietal lobe, although it is also suggested that there could be nuclei of these neurons in other areas such as the insula, the anterior cingulum and the superior temporal gyrus.
Studies conducted with people with autism spectrum disorder (ASD) show the existence of alterations in the activity of their mirror neurons, specifically in the lower frontal gyrus, the insula and the cingulate cortex. These alterations would explain the inability of these people to capture the intentions of others and experience empathy , just as we do in people without ASD.
Research on patients with prefrontal lobe injuries that include lower frontal gyrus has shown that they often have a deficit in inhibiting responses. It has been suggested that there is a centrally located inhibitory mechanism that suppresses irrelevant responses, and that such inhibition would be located primarily in the right lower frontal gyrus.
On the other hand, the same inhibitory control mechanism seems to be altered in patients with obsessive-compulsive disorder (OCD) . In a study comparing healthy subjects with individuals with this disorder, significant alterations were found in structural connectivity, probably associated with a lack of myelination and axonal problems in the lower frontal gyrus of patients with OCD .
Finally, it has been found that the lesions in the Broca area, which corresponds to Brodmann area 44 and area 45 (opercular pair and triangular pair of the lower frontal gyrus in the left hemisphere, respectively) involve linguistic difficulties such as those presented below:
- Problems in generating and extracting meaning from actions.
- Difficulties in sequencing motor and expressive elements
- Semantic and syntactic problems.
- Language impoverishment. In extreme cases there may be akinetic mutism or hypolalia (decreased or delayed verbal expression).
- Decreased verbal fluency, both in phonological and semantic tasks.
- Inability to understand sayings or idioms.
- Ardila, A. (2012). Prefrontal cortex, language and executive functions. In Neuropsychology of the prefrontal cortex and executive functions (pp. 299-314).
- Aron A.R., Robbins T.W., Poldrack R.A. Inhibition and the right inferior frontal cortex. Trends Cogn. Sci. 2004;8:170-177.
- Hampshire, A., Chamberlain, S. R., Monti, M. M., Duncan, J., & Owen, A. M. (2010). El papel del giro frontal inferior derecho: inhibición y control de la atención. Neuroimage, 50(3), 1313-1319.