Critical periods: Is it really impossible to modify a neocortex?

One of my ardors is adult learning, and I think if the learning process strongly correlates with the degree of neuronal binding, creating a new neuronal path and enhancing the strength of neuronal connections are pivotal to accelerate the efficiency of adult learning. However, I found a new research related to my interest. That is “critical periods” in our brain. Singer (2008) describes this idea in the following: “Once the respective developmental window close, neurons stop forming new connections and existing connections can no longer be removed” (p. 101). According to the author’s explanation, especially, our neocortex which is involved in higher functions such as reasoning, thoughts, and language can’t be modified once critical period is over. I’m looking for the way to modify the neocortex though it is said impossible to modify it after critical periods.
Reference

The Educated Brain: Essays in Neuroeducation

Getting Started with Neurofeedback: Traditional psychotherapy VS Neurotherapy

I've never heard of "neurotherapy" before, so I was intrigued by this new kind of therapy and read a book about this.

Traditional psychotherapy has mainly two intervention tools: talk and medication. Of course, talk therapy has been an effective modality even now, but the result tends to be subjective. Furthermore, medication can’t exclude a possibility of side effects though it changes our brain activity directly. Against this backdrop, neurotherapy has drawn attention as a new type of psychotherapy. Neurotherapy has a unique modality, neurofeedback. In a word, the characteristic of neurofeedback is that it “is similar to a comprehensive exercise program because it strengthens neural pathways while increasing mental endurance and flexibility” (Demos, 2005, p. 5). As mentioned above, the traditional psychotherapy has faced a challenge to reveal the effect explicitly, and, in fact, this is one of the limitations in the traditional psychotherapy. However, I think that neurotherapy will play a key role to connect the subjective assessments with the objective effects by using the neurofeedback system.